Signaling system with adaptive timing calibration

ABSTRACT

A signaling system is disclosed. The signaling system includes a first integrated circuit (IC) chip to receive a data signal and a strobe signal. The first IC includes circuitry to sample the data signal at times indicated by the strobe signal to generate phase error information and circuitry to output the phase error information from the first IC device. The system further includes a signaling link and a second IC chip coupled to the first IC chip via the signaling link to output the data signal and the strobe signal to the first IC chip. The second IC chip includes delay circuitry to generate the strobe signal by delaying an aperiodic timing signal for a first time interval and timing control circuitry to receive the phase error information from the first IC chip and adjust the first time interval in accordance with the phase error information.

RELATED APPLICATIONS

This application is a Continuation of U.S. Ser. No. 16/584,830, filedSep. 26, 2019, titled SIGNALING SYSTEM WITH ADAPTIVE TIMING CALIBRATION,which is a Continuation of U.S. Ser. No. 15/250,685, filed Aug. 29,2016, titled SIGNALING SYSTEM WITH ADAPTIVE TIMING CALIBRATION, now U.S.Pat. No. 10,447,465, which is a Continuation of U.S. Ser. No.13/301,383, filed Nov. 21, 2011, titled SIGNALING SYSTEM WITH ADAPTIVETIMING CALIBRATION, now U.S. Pat. No. 9,432,179, which is a Continuationof U.S. Ser. No. 11/384,148, filed Mar. 16, 2006, titled SIGNALINGSYSTEM WITH ADAPTIVE TIMING CALIBRATION, now U.S. Pat. No. 8,121,237,all of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to high-speed signaling systems.

BACKGROUND

Strobe signals are commonly used to control data transfer in high-speedsignaling systems. In a typical arrangement, a transmitting deviceoutputs a data signal onto a data line and simultaneously toggles astrobe signal on a corresponding strobe line to indicate the datatransfer. The data and strobe signals propagate together to a recipientdevice which samples the data signal in response to the strobe signaltransition.

For reliable operation, the data and strobe signals should arrive at therecipient device in a relatively precise phase relationship so thatstrobe-responsive sampling will occur at the desired sampling instant.Phase error between the data and strobe signals resulting frompropagation-time differences on the strobe and data lines or fromoperational variations in the strobe and data signal drivers orreceivers may cause the data signal to be sampled at a non-optimalpoint, reducing signaling margin and increasing the likelihood of biterrors.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1A illustrates an embodiment of an integrated circuit device havingcircuitry to adaptively compensate for static and dynamic phase errorsbetween an incoming timing signal and a desired sampling instant in acorresponding data signal;

FIG. 1B illustrates an exemplary phase relationship between the strobesignal and data signal described in reference to FIG. 1A;

FIG. 2 illustrates a more detailed embodiment of an integrated circuitdevice having adaptive timing calibration circuitry;

FIG. 3A illustrates an exemplary positive and negative data sample pairand intervening edge sample that collectively form a phase-errorindicator;

FIG. 3B illustrates exemplary error counting operations that result fromcomparisons of the edge sample and data sample pair of FIG. 3A;

FIG. 4 is an exemplary timing diagram for the adaptive timingcalibration circuitry of FIG. 2;

FIG. 5 illustrates an embodiment of an integrated circuit device havingadaptive timing calibration circuitry similar to that of FIG. 2, exceptthat propagation delay adjustments are made in proportion to themagnitude of the phase error detected in a given integration period,rather than incrementally;

FIG. 6 illustrates an embodiment of an integrated circuit device havingadaptive timing calibration circuitry similar to that of FIG. 2, butincluding additional logic to ensure that a threshold number of phaseerror indications are obtained before adjusting the applied delaycontrol value;

FIG. 7 illustrates an embodiment of an integrated circuit device havingadaptive timing calibration circuitry similar to that of FIG. 2, butwith subrate loop operation;

FIG. 8 is an exemplary timing diagram illustrating operation of thesubrate timing calibration loop of FIG. 7 according to an embodimenthaving a divide-by-4 loop rate;

FIG. 9 illustrates an embodiment of an integrated circuit device 320that receives a strobe signal per byte of data signals, and thatincludes adaptive timing calibration circuitry to delay the strobesignal as necessary to establish the data sampling point at the medianof the ideal sampling times for the incoming data signals;

FIG. 10 illustrates an embodiment of an integrated circuit device thatreceives a strobe signal per byte of data signals as in FIG. 9, and thatincludes adaptive timing calibration circuitry to delay both the strobesignal and the incoming data signals as necessary to sample each of thedata signals at a respective desired sampling instant;

FIGS. 11A-11D are exemplary timing diagrams that illustrate the adaptivetiming calibration approach described in reference to FIG. 10;

FIG. 12 illustrates a memory system having a memory controller and amemory subsystem that employ the above-described adaptive timingcalibration techniques to establish and maintain desired phaserelationships between various data, strobe, control and clock signals;

FIG. 13 illustrates an exemplary embodiment of the data-strobe receiveinterface with adaptive timing calibration circuitry within the memorycontroller of FIG. 12 and its interconnection to a memory device;

FIG. 14 illustrates a distribution of adaptive timing calibrationcircuitry between the memory controller and a memory device of FIG. 12to support adaptive timing calibration of the clock, data and requestsignals transmitted from the memory controller to the memory device;

FIG. 15 illustrates an embodiment of an oversampling data receiver thatmay be used to implement each of the oversampling data receivers of FIG.14;

FIG. 16 illustrates an embodiment of an oversampling request receiverthat may be used to implement the oversampling request receiver of FIG.14;

FIG. 17A illustrates an exemplary embodiment of a phase-compensatingdata/strobe transmitter that may be used to implement each of thephase-compensating transmitters of FIG. 14;

FIG. 17B illustrates an exemplary embodiment of a phase-compensatingrequest/clock transmitter that may be used to implement thephase-adjusting request transmitter of FIG. 14;

FIG. 18 illustrates an exemplary adaptive calibration sequence that maybe applied within the memory system of FIG. 13 to establish a desiredphase alignment between signals transmitted from the memory controllerto the memory devices;

FIG. 19 illustrates an embodiment of a strobe enable circuit that may beused to implement the strobe enable circuit of FIG. 13;

FIG. 20 illustrates a delay-locked loop circuit that may be used togenerate control signals for establishing quadrature delay in aquadrature delay element; and

FIG. 21 illustrates an exemplary embodiment of a variable delay circuitthat may be used to implement strobe delay circuits and data delaycircuits.

DETAILED DESCRIPTION

A signaling system that adaptively compensates for phase errors betweendata signals and corresponding sample-timing signals is disclosed invarious embodiments. In one embodiment, an incoming timing signal ispassed through a variable delay circuit to provide a sampling signalthat is used, in turn, to oversample an incoming data signal and therebyobtain phase error information. The phase error information is appliedto iteratively adjust the propagation delay through the variable delaycircuit and thus to adaptively compensate for phase errors between thetiming signal and data signal, including static phase errors that resultfrom signal propagation-time differences and operational variationsbetween signal drivers and receivers and dynamic phase errors thatresult from gradual changes in voltage and temperature or other sourcesof run-time phase drift.

FIG. 1A illustrates an embodiment of an integrated circuit (IC) device100 having circuitry to adaptively compensate for static and dynamicphase errors between an incoming timing signal 104 and a desiredsampling instant in a corresponding data signal 102. In the embodimentof FIGS. 1A and 1 n other exemplary embodiments described herein, theincoming timing signal is a strobe signal, meaning an aperiodic timingsignal that is toggled between upper and lower signaling levels tosignal the presence of valid data on one or more associated data lines.In alternative embodiments, including each of the embodiments describedherein, the incoming timing signal may be a clock signal instead of astrobe signal. Also, unless context indicates otherwise, the expressiondata is used generically herein to refer to masking information, commandor request values, configuration information, error-checking and/orcorrecting information or any other type of information to becommunicated over a signaling link.

In the embodiment of FIG. 1A, IC 100 includes input nodes 101 and 103,strobe receiver 105 (DQS Rx), strobe delay circuit 107 (DQS Delay),oversampling data receiver 109 (Oversampling DQ Rx) and adaptive timingcontrol circuit 111 (Adaptive Timing Control). The input nodes 101 and103 of the IC device 100 are provided to receive the data signal (DQ)and strobe signal (DQS) via respective data and strobe lines (102, 104)that collectively form a strobe-timed signaling link. Though depicted ascontact pads, the input nodes 101, 103 may be any type of structure forreceiving an incoming signal including, without limitation, contactlessinterconnects for receiving inductively or capacitively conveyed inputsignals.

The nominal phase alignment between the incoming strobe and data signalsmay vary depending on the signaling protocol and the role of the ICdevice 100 within the signaling system. In a number of embodimentsdescribed herein, for example, the strobe signal may arrive at the ICdevice 100 in either edge-alignment or quadrature-alignment with dataeyes in the incoming data signal (i.e., data-valid intervals) as shownin FIG. 1B. Furthering the example, the IC device 100 is assumed to bepart of a double data rate signaling system in which data is transmittedduring both even and odd phases of a transmit clock cycle (e.g., an evenphase of the transmit clock cycle may be referenced to a rising edgetransition of a transmit clock signal, and an odd phase of the transmitclock cycle may be referenced to a falling edge of the transmit clocksignal), thus delivering two data values, even and odd, to the IC device100 per transmit clock cycle. Selecting the transmit clock cycle time asa reference period and the opening edge of the even data eye as a 0°point, then edge-aligned strobe signal transitions occur nominally at 0and 180° as shown in FIG. 1B, while quadrature-aligned strobe signaltransitions occur nominally at 90 and 270°, at the midpoints of the dataeyes. Double data rate signaling and data-edge-referenced phase notationis assumed in a number of the embodiments described below, though anyother data rates may be used in alternative embodiments (e.g., thenumber of data values per transmit clock cycle may be 1, 4, 8, 10, 16 orany other desirable value) and phase angles may be referenced to anyuseful reference point. Also, in IC device 100 and other embodimentsdescribed below, the ideal sampling instant is assumed for simplicity tooccur at the midpoint of each data eye (i.e., at quadrature alignment toedges of the data eye), though the ideal sampling instant may be offsetfrom the date eye midpoint in various embodiments to account fordifferences between receiver setup and hold times or where maximumeye-opening is offset from the midpoint.

Still referring to FIG. 1A, in systems in which the strobe line 104 isshared by two or more devices (e.g., where IC device 100 both receivesand transmits strobe signals on the strobe line 104 as in abidirectional signaling arrangement), the strobe line 104 may be drivento a predetermined level at the conclusion of a given transmission,thereby relinquishing the strobe line 104 for use by one or more otherdevices. Such operation is referred to herein as parking the strobe lineand, in one embodiment, involves charging the strobe line 104 (orenabling the strobe line to be charged) to a midpoint level so that aninitial transition from the midpoint level to an upper or lower signallevel will not trigger a data sampling operation in the recipientdevice, but rather acts as a start-of-transfer signal to indicate thatone or more data-sampling transitions of the strobe signal areforthcoming. Accordingly, when applied in such an embodiment, the strobereceiver 105 may include circuitry to detect start-of-transferindications and, in response, pass subsequent strobe signal transitionsto downstream circuitry in the form of a clean strobe signal 106(DQS_clean). In applications that do not require strobe line parking(e.g., strobe line 104 is not driven by more than one device), thestrobe receiver 105 may be implemented, for example, by a simple bufferamplifier or omitted altogether.

In one embodiment, the strobe delay circuit 107 is a variable-delaycircuit having a propagation delay selected from a range of propagationdelays in accordance with a delay control value 114 (DVal). Thus, thestrobe delay circuit delays the clean strobe signal according to thedelay control value to yield a clean, delayed strobe signal referred toherein as a sampling signal 108 (sample). In one embodiment, the strobedelay circuit is implemented by a variable delay line that exhibits arange of propagation delays centered around a nominal data samplinginstant. For example, in an embodiment in which an edge-aligned strobesignal is received, the propagation delay range may center around360°/2n, where ‘n’ is the data rate, thus placing the sampling signal108 at the nominal midpoint of data eyes in the incoming data signal.Thus, in the case of an edge-aligned strobe signal in a double data ratesignaling system as shown in FIG. 1B, the propagation delay range may becentered around 90° to place the sampling signal 108 nominally at thedesired sampling point. In the case of a quadrature-aligned strobesignal 104, the incoming strobe signal is already nominally aligned withthe data eye midpoint. In such cases, a small delay, a, may beintroduced in the data signal path either in the transmit device or inIC 100 (or both) to enable the nominal propagation delay of the strobedelay circuit 105 to be centered around a, thus providing headroom foradvancing the propagation delay of the strobe signal 104 relative to thedata signal 102. The range of propagation delays may be selectedaccording to a maximum expected phase error in the incoming strobesignal, or to allow a full range of correction, or correction up to±360°/2n, where n is the data rate.

The oversampling data receiver 109 samples the incoming data signal 102in response to the sampling signal 108 to generate a sequence of datasamples 110, and additionally samples the incoming data signal 102 inresponse to a phase-shifted version of the sampling signal that isnominally edge-aligned with the data signal thereby providing a sequenceof edge samples. Accordingly, the data signal 102 is said to beoversampled, meaning sampled more frequently than the rate at whichsymbols are conveyed in the signal. In this example in which every otherdata edge is sampled, the oversampling ratio (i.e., ratio of samplescaptured to symbols received) is 3:2. That is, two data samples and anedge sample are captured for each pair of received data bits. In a modein which each data edge is sampled, the oversampling ratio would be 2:1.

In the exemplary double-data rate timing arrangement shown in FIG. 1B,the phase offset between the sampling signal 108 and phase-shiftedversion of the sampling signal is the quadrature offset, 90°.Accordingly, the phase-shifted version of the sampling signal isreferred to herein as a quadrature sampling signal to indicate thedata-eye edge-to-midpoint phase offset relative to the sampling signal,but the phase offset may be smaller or greater than 90°, for example,where different data rates apply and may be a programmably selectedvalue to support multiple data rates.

In one embodiment, the oversampling data receiver 109 compares the dataand edge samples over time to develop a phase error 112 that indicateswhether the edge samples are predominantly captured after or beforecorresponding transitions of the data signal and thus indicates whetherthe sampling signal is early or late relative to a desired samplinginstant (i.e., the data eye midpoint in this example). The phase error112 is supplied to the adaptive timing control circuit 111 which adjuststhe delay control value 114 in accordance with the phase error 112,thereby decreasing or increasing the propagation delay in the strobedelay circuit 107 to adjust the phase of the sampling signal 108 in adirection that counters the phase error 112. Thus, by oversampling theincoming data signal 102 to obtain phase error information and applyingthe phase error information to carry out closed-loop phase adjustment,the propagation delay experienced by the incoming strobe signal 104 maybe adaptively adjusted to maintain the desired data sampling instantdespite run-time changes in voltage and temperature or other sources ofphase drift. Moreover, because of the error-correcting nature of thephase adjustment loop (i.e., negative feedback operation), static orsystematic phase errors that result from chip-to-chip propagation-timedifferences between strobe and data signals or from signaling componentvariations (e.g., drive-strength variations in signal drivers, variationbetween signal line termination components, variations in signalreceiver operation, etc.) may be automatically compensated by thecontinuous adaptive calibration, obviating specializedinitialization-time calibration circuitry and procedures.

Still referring to FIG. 1, it should be noted that instead of delayingthe strobe signal 104 (or clean version thereof) in strobe delay circuit107, the incoming data signal 102 may be delayed in a data delay circuit(not shown) to achieve a desired sample timing relationship. Thus, thedelay control value may be supplied to the data delay and appliedtherein to adjust the phase of the sampled data signal in a directionthat counters the phase error 112.

FIG. 2 illustrates a more detailed embodiment of an IC device 120 havingadaptive timing calibration circuitry. IC device 120 includes inputnodes 101 and 103 for receiving data and strobe signals 102 and 104 (DQand DQS), together with a strobe receiver 125, strobe delay circuit 107,oversampling data receiver 130, and adaptive timing control circuit 150.The strobe receiver 125 includes a buffer amplifier 127 and strobeenable logic 129 to convert a three-level strobe signal (i.e., havinghigh, low and parked signal levels) into a binary, clean strobe signal126 (DQS_clean), and the strobe delay circuit 107 operates generally asdescribed in reference to FIG. 1 to delay the clean strobe signal 126 inaccordance with a delay control value 134 (DVal) to produce samplingsignal 128. The sampling signal 128 is provided, in turn, to theoversampling receiver 130 where it is used to trigger sampling of theincoming data signal. The oversampling receiver 130 is designated “DataCapture & Timing Error Detection” in FIG. 2 to emphasize its dual datacapture and timing error detection roles.

The oversampling receiver 130 includes a buffer amplifier 131 to amplifythe incoming data signal 102 and to supply the amplified signal to dataand edge sampling circuits 133 and 135. The data sampling circuit 133samples the incoming data signal in response to positive and negativeedges of the sampling signal 128 (or, if the sampling signal 128 isgenerated differentially, in response to rising edges of complementarycomponents of the sampling signal) and thus generates (i.e., captures,latches, registers, etc.) a sequence of even and odd data samples, 140 aand 140 b. The even and odd data samples are also referred to herein asleading and lagging samples to indicate their arrival sequence at the ICdevice, and as positive and negative data samples to emphasize thesampling signal transitions that trigger their capture. The edgesampling circuit 135 samples the incoming data signal in response to aquadrature sampling signal 138, a version of the sampling signal 128that is phase shifted by delay element 137 (shown in this example as a90° delay element, but more generally implemented by a 360°/2n delayelement, where n is the data rate) to establish a sampling pointnominally aligned with transitions in the incoming data signal, and thusgenerates a sequence of edge samples 142 that correspond to the sequenceof data samples 140 a, 140 b (collectively, 140) generated by datasampling circuit 133.

Referring to FIG. 3A, each positive and negative data sample pair andintervening edge sample collectively form a phase-error indicatorreferred to herein as a tri-sample. That is, if a data transition hasoccurred (i.e., positive sample (PS) not equal to negative sample (NS)),then the edge sample (ES) will match the positive sample if thequadrature sampling signal transitions early relative to data signaltransition and will match the negative sample if the phase-shiftedsampling signal transitions late relative to the data signal transition.Accordingly, referring to FIGS. 2 and 3A, if the edge sample andpositive sample do not match (ES< >PS), the quadrature sampling signal138 and therefore the sampling signal 128 are deemed to be late relativeto their desired sampling times and a positive error 146 (i.e.,positive-sample mismatch, pErr) is signaled by exclusive-OR gate 145 toindicate the late condition. If the edge sample and negative sample donot match (ES< >NS), the quadrature sampling signal 138 and samplingsignal 128 are deemed to be early relative to their desired samplingtimes, and a negative error, nErr, is signaled by exclusive OR gate 147to indicate the early condition. Note that, in the embodiment of FIG. 2and any other embodiments described herein, falling edges of thequadrature sampling signal may also be used to sample the incoming datasignal at the transition between odd and even data eyes, and thusdoubling the edge sampling rate and, accordingly, the rate at whichphase error information is gathered.

In the embodiment of FIG. 2, a signed counter 149, referred to herein asa phase error counter or error counter, is provided to adjust an errorcount at each rising edge of the sampling signal 128 according to thephase error indicated by exclusive-OR gates 145 and 147 (collectivelyreferred to herein as error logic gates) in response to the tri-samplecaptured at the preceding rising and falling edges of the samplingsignal 128 and at the rising edge of the quadrature sampling signal 138.Referring to FIG. 3B, for example, if a negative error is signaled(nErr=1, pErr=0), the error count is decremented and if a positive erroris signaled (pErr=1, nErr=0), the error count is incremented. By thisoperation, the error count constitutes a differential error value thatindicates the difference between the number of positive and negativeerrors detected over a given time interval. The sign of the error countindicates whether the majority of errors are positive or negative (i.e.,sampling late or early) and the magnitude of the error count indicatesthe magnitude of the phase error. Still referring to FIG. 3B, the errorcount remains unchanged if no phase error is signaled (nErr=pErr=0) orif both phase errors are signaled (nErr=pErr=1), the final case being aninvalid condition in which a bit error may be inferred. Additionallogic, not shown, may be provided to track bit errors indicated by theerror logic gates and to and take corrective action (e.g., if athreshold number of bit errors are detected per unit time), or notifythe transmitting device of the error status. In one embodiment, forexample, the IC device 120 may negotiate a reduced signaling rate withthe transmitting IC in response to detecting a threshold number of biterrors within a given time interval. Alternatively or additionally, theIC device 120 may adjust signal reception parameters (or request thetransmitting IC to adjust signal transmission parameters) including, forexample and without limitation, equalization parameters, decisionthreshold levels used to distinguish logic ‘1’ and logic ‘0’ signallevels within the sampling circuits 133 and 135 (or either one of them)or any other parameters that may be adjusted to reduce the bit errorrate.

Still referring to FIG. 2, the adaptive timing controller 150 includesan integration timer 153 that counts sampling signal assertions andraises (or lowers) an update signal 154 upon reaching a threshold countvalue, thus establishing a minimum phase error detection intervalreferred to herein as an integration period. In one embodiment, theintegration timer 153 receives an integration time value 158 (i.e.,specifying a threshold count value) from a one-time or run-timeprogrammable register within IC 120 (not shown), thus allowing theintegration period to be programmed in accordance with system needs. Theintegration period may alternatively be fixed. In either case, theupdate signal 154 is supplied to the error counter 149 to mark thetransition between integration periods. In one embodiment, the errorcounter 149 responds to assertion of the update signal 154 by latching(or registering) the sign of the error count at a sign output (Sign) toprovide an error sign signal 152 and by resetting the error count (e.g.,to zero) in preparation for the ensuing integration period. Thus, theerror sign 152 generated during a given integration period is maintainedat the sign output of the error counter 149 during the subsequent errorintegration period, thereby enabling pipelined operation in which theerror sign 152 for a given integration period, n, is applied to updatethe delay control value 134 while an error sign for subsequentintegration period, n+1, is developed within the error counter 149.

The error sign 152 is supplied to a delay value update circuit 151within the adaptive timing control circuit to generate an updated delaycontrol value 156 (DVal′). In the embodiment of FIG. 2, for example, theerror sign 152 is supplied to a control input of multiplexer 157 toselect an incremented or decremented version of the applied delaycontrol value 134 to be the updated delay control value 156. That is, ifthe error sign 152 indicates that a majority of the phase errorsdetected in the preceding integration period are positive phase errors(e.g., error sign=0), then the sampling signal 128 is deemed to be laterelative to the desired data sampling point so that a decremented delaycontrol value is selected as the updated delay control value 156 toreduce the propagation delay through the strobe delay circuit 107 andthus advance the sampling signal 128 toward the desired sampling point.Conversely, if the error sign 152 indicates that a majority of the phaseerrors detected in the preceding integration period are negative phaseerrors (e.g., error sign=1), then the sampling signal 128 is deemed tobe early relative to the desired sampling point and an incremented delaycontrol value is selected as the updated delay control value 156 toincrease the propagation delay through the strobe delay circuit 107 andthus retard (i.e., delay) the sampling signal 128 relative to thedesired sampling point. In the particular embodiment shown, a delaycontrol storage element 155 (e.g., a register or latch) is provided tostore the applied delay control value 134 (i.e., delay control value,DVal, supplied to the strobe delay circuit 107 during a givenintegration period). As shown, the applied delay control value 134 isalso supplied to arithmetic operators 159 and 161 (e.g., a subtractionor decrementing circuit and an addition or incrementing circuit,respectively) within the delay value update circuit 151. The arithmeticoperators 159 and 161 are coupled to receive an offset value 162 from aprogrammable register and perform an offset subtraction and offsetaddition, respectively, to generate the decremented and incrementeddelay control values supplied to inputs of multiplexer 157. Inalternative embodiments, the offset value 162 may be fixed. Also, theoffset value 162 may be selected, automatically or in response to aprogrammed selection value, from among multiple fixed or programmableoffsets to enable different granularity in the phase error correction tobe selected (e.g., coarse granularity selected initially, finergranularity selected thereafter). Further, separate offset values may beprovided to the arithmetic operators 159 and 161. In any case, theupdate signal 154 is supplied to an enable-input (“en”) of delay controlstorage element 155 so that, when the update signal 154 is asserted, theupdated delay control value 156 selected by multiplexer 157 is loadedinto delay control storage element 155, thereby establishing a new delaycontrol value 134 to adjust the propagation delay in the strobe delaycircuit 107.

FIG. 4 is an exemplary timing diagram for the adaptive timingcalibration circuitry of FIG. 2. As shown, an input data signal (DataIn) includes even and odd data eyes, De and Do, in successivetransmission intervals. Even data eye, De, is sampled in response to arising edge 175 of the sampling signal (sample) to provide even datasample, PS (i.e., positive sample), and odd data eye, Do, is sampled inresponse to the subsequent falling edge 177 of the sampling signal toprovide odd data sample, NS (negative sample). The transition betweenthe even and odd data eyes is sampled in response to rising edge 180 ofthe quadrature sampling signal (qsample) to provide an edge sample, ES,that, when combined with the even and odd data samples, completes atri-sample for the current sampling cycle. As discussed above, the edgesample and even sample are compared to generate positive error signal,pErr, and the edge sample and odd sample are compared to generatenegative error signal, nErr. At the rising sampling signal edge 179immediately following capture of the tri-sample, the phase errorindicated by the positive and negative error signals is integrated(i.e., accumulated) into the error sum, Esum, for integration period“n”; an operation indicated at 181. Thereafter, at the conclusion ofintegration period n, the sign of the error count is latched (orregistered) and applied during subsequent integration period n+1, asshown at 183, to generate an updated delay control value, DVal′(n). Asshown at 185, at the start of integration period n+2, the updated delaycontrol value is latched (or registered) as the delay control value,DVal, applied during that period to control the propagation delay of thestrobe delay circuit.

Referring to FIGS. 2 and 4, it can be seen that the applied delaycontrol value 134 for a given integration period, n, corresponds to theerror sign generated during integration period n−2, and thus is appliedtwo integration periods after the corresponding phase errors weredetected. This loop latency results, in part, from the latent error signoutput from the error counter and also due to latent selection of theupdated delay control value in response the error sign. Loop latency maybe reduced in alternative embodiments, for example, by applying theerror sign generated during given integration period at the conclusionof that interval to deliver an updated delay control value to the strobedelay circuit.

FIG. 5 illustrates an embodiment of an IC device 200 having adaptivetiming calibration circuitry similar to that of FIG. 2, except thatpropagation delay adjustments are made in proportion to the magnitude ofthe phase error detected in a given integration period, rather thanincrementally. Thus, the strobe receiver 125, strobe delay circuit 107,data signal amplifier 131, data and edge sampling circuits 133 and 135,quadrature delay element 137, error logic gates 145 and 147, integrationtimer 153, and delay control storage element 155 all operate generallyas described in reference to FIG. 2. Error counter 205 also operatessimilarly to the error counter 149 described in reference to FIG. 2,but, instead of outputting only the sign of the differential error value(i.e., error count) developed over a given integration period, errorcounter 205 outputs the entire differential error value 206 (dErr), forexample, as a signed numeric value. In the particular embodiment shown,the differential error value 206 generated within data capture andtiming error detection circuit 201 is supplied to a multiplier circuit209 within adaptive timing control circuit 203 which multiplies thedifferential error value 206 by a programmable scale factor 214 togenerate a phase correction value 216. The phase correction value 216 issupplied, in turn, to arithmetic circuit 211 which subtracts the phasecorrection value 216 from the applied delay control value 134 (DVal) togenerate updated delay control value 212 (DVal′). By this operation, anegative differential error value 206, indicating that transitions ofquadrature sampling signal 138 are predominantly early relative tocorresponding data transitions, will yield an increased updated delaycontrol value 212 to delay the sampling signal 128 and quadraturesampling signal 138. Conversely, a positive differential error value206, indicating that sampling signals are predominantly late, will yielda decreased delay control value to advance the sampling signal. Ingeneral the timing diagram of FIG. 4 applies equally to operation of IC200. As discussed, latency between phase error determination andcorresponding adjustment of the delay control value 134 may be reducedin alternative embodiments, and the incoming data signal mayadditionally be sampled at the transition between odd and even data eyesto more rapidly gather phase error information.

FIG. 6 illustrates an embodiment of an IC device 230 having adaptivetiming calibration circuitry similar to that of FIG. 2, but includingadditional logic to ensure that a threshold number of phase errorindications are obtained before adjusting applied delay control value134. Thus, the strobe receiver 125, strobe delay circuit 107, amplifier131, data and edge sampling circuits 133 and 135, quadrature delayelement 137, error logic gates 145 and 147, integration timer 153, anddelay control storage element 155 operate generally as described inreference to FIG. 2. Phase error logic 235 (i.e., PE Logic, part of datacapture and timing error detection circuit 231) also operates similarlyto the error counter 149 described in reference to FIG. 2, but includesadditional circuitry to compare the total number of phase errorindications generated during a given integration period (i.e., totalnumber of pErr and nErr assertions) with a fixed or programmablethreshold and to generate, according to the comparison result, a validsignal 236 which qualifies or disqualifies the corresponding error sign152. Thus, if the valid signal 236 is true (logic ‘1’ in this example),the error sign 152 is qualified as the result of a sufficient number ofphase error indications and multiplexer 239 within adaptive timingcontrol circuit 233, which receives the valid signal 236 at a controlinput, passes an updated delay control value 156 to the input of thedelay control storage element 155 as the delay control value 234 to beapplied during the next integration period. Conversely, if the validsignal 236 is false (logic ‘0’ in this example), the multiplexer 239passes the applied delay control value 134 back to the input of thedelay control storage element 155 to effect a hold state therein andthus prevent the disqualified error sign 152 from being used to adjustthe applied delay control value 134.

In one embodiment, shown in detail view 240, the phase error logic 235includes an up/down counter 243 that operates as described in referenceto FIG. 2 to generate a differential error count, as well as a monotoniccounter 245 (i.e., up-only or down-only counter) to count the totalnumber of phase error indications. In the particular embodiment shown,the positive and negative phase error signals (pErr and nErr) aresupplied to an OR gate 241 having an output coupled to the count-enableinput of the monotonic counter 245. By this arrangement, when a positiveor negative phase error is signaled (i.e., in signals 146 or 148), theoutput of the OR gate 241 goes high to enable an aggregate phase errorcount 246 within the monotonic counter 245 to be incremented at the nextassertion of the sampling signal 128. The aggregate phase error count246 is supplied to comparator 247 where it is compared with a fixed orprogrammable threshold value 248 to generate a qualifier bit 250. Theupdate signal is supplied to enable inputs (en) of storage elements 249and 251 (e.g., latches or registers) and to the reset (rst) inputs ofthe counters 243 and 245 so that, when the update signal 154 isasserted, the error sign bit 244 and corresponding qualifier bit 250 arecaptured in the storage elements 249 and 251 at the next assertion ofthe sampling signal 128, and the count values within counters 243 and245 are cleared in preparation for the subsequent integration period.The error sign bit and qualifier bit are output from the storageelements 249 and 250 as the sign bit 152 and valid bit 236,respectively.

In an alternative embodiment, the phase error logic 235 may includeseparate monotonic counters (e.g., to count only up or down) to countthe early indications and the late indications, respectively, signaledby the error values 146 and 148, with logic to output a high or lowerror sign bit according to which of the monotonic counters develops ahigher count during a given integration period and to generate a high orlow valid bit according to whether a sum of the counts of the monotoniccounters exceed a fixed or programmed threshold value.

FIG. 7 illustrates an embodiment of an IC device 260 having adaptivetiming calibration circuitry similar to that of FIG. 2, but with subrateloop operation. More specifically, rather than processing phase errorsat the rate of the sampling signal 128 (and thus at the peak datatransfer rate of the signaling system), a frequency-divided version ofthe sampling signal, referred to herein as a subrate sampling signal, isused to time operation of phase error logic 275 and adaptive timingcontrol circuitry 262, thus reducing the rate at which phase errorinformation is gathered and applied to update the sampling signal phasein exchange for reduced loop power consumption and relaxed logic timing.

As shown, IC device 260 includes a strobe signal receiver 125; a strobedelay circuit 107; an oversampling receiver 261 that includes amplifier131, data and edge sampling circuits 133 and 135, error logic gates 145and 147, and phase error logic 235; and an adaptive timing controlcircuit 262 that includes integration timer 153, delay control storageelement 155, and delay control update circuit 237 (having multiplexers157 and 239, and arithmetic operators 159 and 161); all of which operategenerally as described above in reference to FIGS. 2 and 6 to effect anadaptive timing calibration loop. In addition to the aforementionedcomponents, the oversampling receiver 261 includes a divider circuit 263to divide the sampling signal 128 by a subrate factor, N, and thusgenerate a subrate sampling signal 264 (sdiv). In the particularembodiment shown, the subrate sampling signal 264 is supplied to a pulsegenerator formed by edge-triggered storage element 265 (e.g., aflip-flop) and logic AND gate 267, and to the timing inputs of the phaseerror logic 275, integration timer 153 and delay control storageelement. The pulse generator operates to generate a subrate pulse 268every N cycles of the sampling signal 128. More specifically, thesampling signal 128 is supplied to a triggering input of storage element265 while the subrate sampling signal 264 is provided to a data-in nodeof storage element 265 and to a non-inverting input of AND gate so that,when the subrate sampling signal 264 goes high, the logic low output ofstorage element 265 (which is supplied to an inverting input of AND gate267), will cause the output of AND gate 267 to go high until the highstate of the subrate sampling signal 264 is captured in the storageelement at the next rising edge of the sampling signal. Thus, thesubrate pulse 268 is initially low when the sampling signal 128 goeshigh at the start of a tri-sample capture sequence, but goes high duringcapture of the tri-sample and remains high until the next rising edge ofthe sampling signal 128 (i.e., start of a subsequent tri-sample capturesequence). At that point, the subrate pulse 268 goes low and remains lowduring the capture of N−1 tri-samples, before going high again to duringcapture of another tri-sample. Thus, the subrate pulse 268 goes high forone of every N cycles of the sampling signal 128. Accordingly, byproviding the subrate pulse 268 to the enable input (en) of an errorstorage element 269 that is triggered by the sampling signal 128, theerror storage element 269 is enabled to store the positive and negativephase error signals 146 and 148 (i.e., pErr and nErr), generated byerror logic gates 145 and 147 as described above, once every N cycles ofthe sampling signal 128 (i.e., once for every N tri-samples) and thusoutputs positive and negative subrate phase error signals 270 and 272(pErrDiv and nErrDiv). The subrate phase error signals 270 and 272 areapplied within the phase error logic 235 generally as described inreference to FIG. 6 to generate an error sign 276 and valid signal 278at the subdivided loop rate. That, the phase error logic may beimplemented as described in reference to FIG. 6, but receives subratephase error signals 270 and 272 in place of the sampling rate phaseerror signals (146 and 148 in FIG. 6) and is clocked by the subratesampling signal instead of the sampling signal. The adaptive timingcontrol circuit 262 similarly operates as described in reference to FIG.6, but at the reduced loop rate.

FIG. 8 is an exemplary timing diagram illustrating operation of thesubrate timing calibration loop of FIG. 7 according to an embodimenthaving a divide-by-4 loop rate. That is, the subrate sampling signalcycles once for every for cycles of the sampling signal. The input datasignal (Data In), sampling signal (sample), even and odd data samples(Even, Odd), and quadrature sampling signal (qsample) are applied asshown at 290 and described in reference to FIG. 3 to generate positiveand negative error signals, pErr and nErr. The sampling signal isfrequency divided by a factor of 4 to produce the subrate samplingsignal (sdiv) and the subrate pulse (s-pulse) is generated once everyfour cycles of the sampling signal. By this operation, every fourthphase error indication (pErr/nErr marked by shading in FIG. 8) iscaptured within the error storage element (i.e., element 269 of FIG. 7)as shown at 294 in response to the rising sampling signal edge thatcoincides with the falling edge of the subrate pulse (i.e., as shown at292), and output to the phase error logic as subrate phase errorsignals, pErrDiv and nErrDiv. The update signal, error accumulation,updated differential error signal (dErr or sign) and updated delaycontrol value have the same timings with respect to each other as inFIG. 3, but are processed at the reduced loop rate.

FIG. 9 illustrates an embodiment of an integrated circuit device 320that receives a strobe signal 104 per byte of data signals 102 ₀-102 ₇(collectively, 102), and that includes adaptive timing calibrationcircuitry to delay the strobe signal 104 as necessary to establish thedata sampling point at the median of the ideal sampling times for theincoming data signals 102. The incoming strobe signal 102 is received instrobe receiver 125 to generate a clean strobe signal 126, then delayedin strobe delay circuit 107 generally as described in reference to FIG.2. The delayed strobe signal 322 is supplied to a clock driver circuit321 to generate a sampling signal 328 (or multiple instances of thesampling signal 328, if necessary to accommodate signal fan-out) that issupplied to oversampling receivers 340 ₀-340 ₇ (collectively 340) foreach of the corresponding data lines 102 ₀-102 ₇. The oversamplingreceivers 340 are also referred to herein as data slice receivers (i.e.,slice 0 data receiver 340 ₀-slice 7 data receiver 340 ₇ as designated inFIG. 9), as each of the data lines may be viewed as corresponding to aslice of a data signaling path.

Continuing with the output of the strobe delay circuit 107, the delayedstrobe signal 322 is also passed through a quadrature delay element 137and supplied to corresponding clock driver circuit 323 to generate aquadrature sampling signal 330 (qsample) and is also passed through adivider circuit 263 and clock driver 325 to generate a subrate samplingsignal 332 (sdiv). The sampling signal 328, quadrature sampling signal330 and subrate sampling signal 332 are supplied to each of the dataslice receivers 340, and the subrate sampling signal 332 is additionallysupplied to adaptive timing control circuit 350. The sampling signal328, quadrature sampling signal 330 and subrate sampling signal 332 areused within each of the data slice receivers 340 to perform the datacapture and timing error detection operations described in reference toFIG. 7. Referring to the detail view of the slice 0 data receiver 340 ₀,for example, the sampling signal 328 is supplied to data samplingcircuit 133 to trigger generation of even and odd data samples (140 aand 140 b), and the quadrature sampling signal 330 is supplied to edgesampling circuit 135 to trigger generation of edge samples 142. Asdiscussed in reference to FIG. 2, tri-samples formed by the data andedge samples are evaluated in error logic gates 145 and 147 to generatepositive and negative phase error signals 146 and 148 (pErr and nErr),respectively. Logic circuitry for processing the phase error signals 146and 148, including the logic described in reference to FIG. 7 forgenerating subrate phase error indications (e.g., storage element 265,logic gate 267 and error storage element 269) is disposed within subratephase error logic 335, along with the above-described phase error logic(e.g., 235 of FIG. 7) for integrating the indicated phase errors togenerate valid and sign signals for each integration period. An updatesignal 154 is asserted by an integration timer 153 within the adaptivetiming control circuit 350 as described in reference to FIG. 2(potentially with modified integration time 158 and clocked by thesubrate sampling signal 332 to account for subrate timing), and thesubrate phase error logic 335 within each of the data slice receivers340 ₀-340 ₇ responds by clearing internal count values and outputting arespective updated valid/sign bit pair, 336 ₀-336 ₇ (also designatedVSi[1:0], where i is the index of the data slice receiver 340), to theadaptive timing control circuit 350.

In one embodiment of the adaptive timing control circuit 350, the validbits of the incoming valid/sign bit pairs 336 ₀-336 ₇ are logicallyANDed in gate 353 to produce a composite valid signal 354 (cValid), andthe sign bits are supplied to a majority detection circuit 351 thatoutputs a majority sign 352 (mSign) that is high if the majority of theincoming sign bits are high, and low if the majority of the incomingbits are low. The composite valid signal 354 is supplied to multiplexer239 which operates as described in reference to FIG. 6 to select,according to the composite valid signal, either an updated delay controlvalue 156 or the active delay control value 134 to be passed, as thenext-cycle delay control value 234, to the input of the delay controlstorage element 155. The majority sign 352 is supplied to multiplexer158 which operates as described in reference to FIG. 6 to generate aupdated delay control value 156. Because the majority sign 352 signals apositive phase error or negative phase error according to the majorityindication of the incoming sign bits, the delay control value 134 isupdated accordingly to adjust the propagation delay within the delaycontrol circuit 107 in a direction counter to the majority error. Bythis operation, the phase of the sampling signal 328 is adaptively phaseshifted to the median of the ideal sampling points within the data slicereceivers 340. Note that while eight data lines 102 and correspondingdata slice receivers 340 are specifically depicted in FIG. 9, there maybe more or fewer data lines and data slice receivers per strobe line inalternative embodiments. Also, despite designation as data lines,various types of information may be carried on the signal lines (or anysubset thereof) that correspond to a give strobe line including, withoutlimitation masking information (e.g., indicating, for example, whetherthe corresponding data is to be masked when stored in a storage array),parity information, error correction code information, command orrequest information, configuration information and so forth.

FIG. 10 illustrates an embodiment of an integrated circuit device 360that receives a strobe signal per byte of data signals as in FIG. 9, andthat includes adaptive timing calibration circuitry to delay both thestrobe signal and the incoming data signals as necessary to sample eachof the data signals at a respective desired sampling instant. As in theembodiment of FIG. 9, the IC device 360 includes input nodes 103 and 101₀-101 ₇ to receive, respectively, a strobe signal 104 and data signals102 ₀-102 ₇. The strobe signal 104 is received and cleaned in the strobesignal receiver 125, delayed in strobe delay circuit 107 and thendistributed (via quadrature delay element 137, divider 263 and clockdrivers 321, 323 and 325) to data slice receivers 361 ₀-361 ₇ in theform of a sampling signal 328 (sample), quadrature sampling signal 330(qsample) and subrate sampling signal 332 (sdiv) generally as describedabove.

Each of the data slice receivers 361 ₀-361 ₇ includes an amplifier 131,sampling circuits 133 and 135, error logic gates 145 and 147 and subratephase error logic 335 which operate generally as described in referenceto FIG. 9 to generate a sequence of tri-samples (each including an evenand odd data sample 140 a and 140 b, and an edge sample 142), integratea phase error value according to the tri-samples (or subrate-selectedset of tri-samples), and signal the phase error to the adaptive timingcontrol circuit in the form of a sign/valid bit pair. Each of the datareceivers additionally includes a data delay circuit 363 coupled betweeninput amplifier 131 and sampling circuits 133 and 135 to enable theincoming data signals 102 ₀-102 ₇ to be delayed by respective delaysbefore being sampled in response to the sampling signal 328 andquadrature sampling signal 330. The data delay circuit 363 within eachof the data slice receivers 361 ₀-361 ₇ exhibits a propagation delayselected from a range of propagation delays in response to a respectivedata delay value received from adaptive timing control circuit 370, thusenabling the adaptive timing control to shift the phase of the sampleddata signals (i.e., the delayed data signals output from respective datadelay circuits 363) relative to one another and relative to the samplingclock signal 328 and quadrature sampling clock signal 330.

The adaptive timing control circuit 370 includes an integration timer153 and delay control update circuit 237 (i.e., including multiplexers239, 157 and arithmetic circuits 159 and 161) which operate generally asdescribed in reference to FIG. 9, but, in contrast to the FIG. 9embodiment, includes multiple delay control storage elements 375 ₀-375 ₈to store respective delay control values that are applied to controlpropagation delays in the data delay circuits 363 of data slicereceivers 361 ₀-361 ₇ and in the strobe delay circuit 107. In theembodiment of FIG. 10, the adaptive timing control circuit 370 furtherincludes a time slice controller 371 and error multiplexing logic 373 toenable time-multiplexed processing of the phase errors 366 ₀-366 ₇(i.e., valid/sign bit pairs, VS0[1:0]-VS7[1:0]) provided by the dataslice receivers 361 ₀-361 ₇. In the particular embodiment shown, each ofthe phase error bit pairs VS0[1:0]-VS7[1:0] is supplied to a respectiveinput port of an error multiplexer 391 within the error multiplexinglogic 373, and additionally to logic gates 393 and 395 which generate acomposite phase-error bit pair 396. More specifically, logic gate 395combines the sign bits in a logic OR combination and therefore generatesa logic ‘1’ composite sign bit so long as at least one of the input signbits indicates that the sampling signal is early relative to the desiredsampling instant for that data slice receiver (i.e., so long as at leastone of the input sign bits is high). Thus, the composite sign bit tracksthe state of the sign bit for the data slice receiver 361 having thelatest desired sampling instant, referred to herein as the most latentdata slice receiver. Logic gate 393 combines the valid bits in a logicAND combination and thus generates a composite valid signal thatqualifies the composite sign bit as valid when each of the data slicereceivers 361 ₀-361 ₇ indicate that their respective sign bits arevalid.

Still referring to FIG. 10, the time slice controller 371 receives aninterval-complete signal 368 from integration timer 153 (marking theconclusion of an integration period) and responds by outputting aone-hot update value 392 (Update[8:0]), and by outputting a one-hotphase select value 378 (PSel[8:0]) to select a valid/sign bit pair (382,384) via error multiplexer 391 (i.e., a phase error signal 366 ₀-366 ₇from one of the data slice receivers or from the compositing logic gates393, 395) and an active one (374) of the delay control values 376 ₀-376₈ via multiplexer 377 to be applied within delay control update circuit237 to generate an new delay control 372. Individual bits of the updatevalue are coupled to the respective enable inputs of the delay controlstorage elements 375 ₀-375 ₈ so that, at the conclusion of theintegration period in which the new delay control value 372 isgenerated, the appropriate bit of the update value 392 may be raised(i.e., as the one-hot bit of the set of bits) to load the new delaycontrol value 372 into a selected one of the delay control storageelements 375 ₀-375 ₈. Thus, the time slice controller 371 providescontrol over which of the delay control values 376 supplied to thevarious delay control circuits 363 and 107 is updated at the conclusionof a given integration period.

In one embodiment, the time slice controller 371 includes state logic(e.g., as in a finite state machine) that operates to initially adjustthe delay within the strobe delay circuit 107 (i.e., adjusting the delaycontrol value 376 ₈) until the sampling signal 328 is aligned with thedesired sampling instant of the most latent data slice receiver 361.Thereafter, the time slice controller 371 leaves the delay control value376 ₈ for the strobe delay circuit unchanged and begins one-by-one(i.e., round-robin) adjustment of the delay control values 376 ₀-376 ₇supplied to the data delay circuits 363 within the data slice receivers361 to align the desired sampling instant for each of the incoming datasignals 102 with the sampling signal 328. In the embodiment of FIG. 10,the time slice controller 371 outputs the phase select value in aone-hot state (i.e., one bit of PSel[8:0] is high) to select theparticular delay control value 376 to be updated at the next assertionof the interval-complete signal 368, then asserts the update signal 392in a one-hot state to load an updated delay control value into acorresponding delay control storage element 375 and to latch a newvalid/sign value (and reset error counters) within the subrate phaseerror logic 335 of the corresponding data slice receiver 361. In thecase of the strobe delay circuit 107, the time slice controller raisesPSel[8] to select delay control storage element 375 ₈ to source theactive delay control value to the delay control update circuit 237(i.e., to the arithmetic logic circuits 159 and 161, and tohold-multiplexer 239), and, when the interval-complete signal 368 isasserted by the integration timer 153, raises Update[8] to load the new(i.e., updated or held) delay control value 372 into delay controlstorage element 375 ₈. In contrast to the delay control values 376 ₀-376₇ for the data delay circuits 363 which are generated in response to thevalid/sign bit pair from a corresponding one of the data slice receivers361, the strobe delay control value 376 ₈ is generated, at least in theembodiment of FIG. 10, based on the composite valid/sign bit pair 396and thus based on the phase error signals 366 from all the data slicereceivers 361. Accordingly, in the embodiment of FIG. 10, the phaseerror logic circuit 335 within each of the data slice receivers 361₀-361 ₇ is updated (i.e., latch updated sign/valid bit pair at outputand reset internal counters) in response to assertion of Update[8]. Asshown, OR gates 367 ₀-367 ₇ are provided to OR signal Update[8] withsignals Update[7]-Update[0], respectively, to generate the signalsapplied to the update inputs of the phase error logic circuits 335within data slice receivers 361 ₀-361 ₇.

FIGS. 11A-11D are exemplary timing diagrams that illustrate the adaptivetiming calibration approach described in reference to FIG. 10. In theparticular example shown, the incoming strobe signal is initiallynominally edge-aligned with the incoming data signals as depicted inFIG. 11A. Thus, to achieve a quadrature relationship between themidpoint of the data eyes and a phase-delayed strobe signal (i.e., thesampling signal), the strobe delay should eventually settle at 90° plusor minus an adaptively determined phase offset. Accordingly, to ensurethat the sampling signal is phase advanced relative to the latest of theincoming data signals, the strobe delay is initially set to delay thesampling signal by 45° as shown in FIG. 11A, thus allowing the strobedelay to be adaptively increased and thereby shifted toward the eventualsettling point. Also, to provide a level of phase-advance headroom forthe data signals, the data signal delays are initially set to delay thedata signals by 10° relative to the incoming strobe signal edge. Otherinitial phase angles (i.e., delay selections) may be established for thestrobe and data signals in alternative embodiments. Also, while notspecifically shown, host-instructed write and/or read access to thedelay control storage elements may be provided to enable initial delaycontrol values to be written therein in response to host instructions orto enable the delay control values to be read out, for example, asstatus information to support run-time configuration decisions and/ordevice testing.

Referring to FIGS. 10 and 11, the time slice controller 371 initiallyraises PSel[8] to enable the delay control value 376 ₈ for the strobedelay circuit 107 to be adjusted and responds to each assertion of theinterval-complete signal 368 by asserting Update[8], thereby enabling anupdated delay control value to be captured within delay control storageelement 375 ₈ and updating the phase error logic circuits 335 (i.e.,latching sign/valid bit pairs and clearing internal counters) withineach of the data slice receivers 361. As shown in FIG. 11B, thisoperation iteratively (adaptively) adjusts the phase of the samplingsignal toward alignment with the latest of the delayed data signals.

In one embodiment, the time slice controller 371 monitors the compositevalid/sign bit pair 396 to determine when the sampling signal reachesalignment with the latest of the delayed data signals (e.g., bydetecting dithering of the composite sign bit, as qualified by thecomposite valid bit) and, upon detecting the desired phase alignment,switches to a data-delay mode in which the delay control values 376₀-376 ₇ for the data delay circuits 363 are adaptively updated toestablish phase alignment between the delayed data signals (or desiredsampling instants thereof) and the sampling signal. In the embodiment ofFIG. 10, for example, the time-slice controller 371 raisesPSel[0]-PSel[7] in round-robin fashion (one after another) in successiveintegration periods to select the delay control value to be updated, andasserts the corresponding one of update signals Update[0]-Update[7] atthe completion of each integration period to load an updated delaycontrol value into the corresponding one of delay control storageelements 375 ₀-375 ₇, and to update the phase error logic 335 within thecorresponding data slice receiver 361. This operation is illustrated inFIG. 11C which depicts the resulting phase shift of delayed data signalstoward alignment with the sampling signal (i.e., the quadrature samplingsignal (qsample) is edge-aligned with the delayed data signals andsampling signal (sample) is quadrature-aligned with the delayed datasignals) and in FIG. 11D which illustrates the desired alignment betweenthe sampling signal and all the delayed data signals. Once the desiredalignment is reached, timing control circuit 370 adaptively maintainsthe desired alignment over gradual changes in voltage and temperature.

Still referring to FIGS. 10 and 11, it should be noted that numerousfeatures and options may be implemented within the adaptive timingcalibration circuitry of IC device 360 in alternative embodiments. Forexample, the time slice controller 371 may include circuitry (e.g.,state machine circuitry or microcontroller circuitry) to interruptround-robin processing of the phase errors 366 signaled by the dataslice receivers 361 in response to detecting an invalid signal (e.g.,valid signal low) for the data slice receiver presently being serviced.That is, instead of proceeding to service the next data slice receiver,the time-slice controller 371 may repeat selection of the data slicereceiver that yielded the invalid phase error 366 in the ensuingintegration period. More generally, instead of time-multiplexedprocessing of the phase errors indicated by the data slice receivers361, the adaptive timing control circuitry 370 may be modified toinclude separate delay control update circuitry for each (or sub-groups)of the data slice receivers 361 ₀-361 ₇, thereby enabling all (orsub-groups) of the data signals to be phase-adjusted in parallel. Aseparate delay control update circuitry may also be provided for thestrobe signal.

FIG. 12 illustrates a memory system 400 having a memory controller 401and a memory subsystem 403 that employ the above-described adaptivetiming calibration techniques to establish and maintain desired phaserelationships between various data, strobe, control and clock signals.In the particular embodiment shown, adaptive timing calibrationcircuitry is distributed between the memory controller 401 and one ormore memory devices 405 that form the memory subsystem 403 so as tolimit the complexity of the more numerous and cost-sensitive memorydevices 405 and thus dispose the error processing and adaptive timingcontrol circuitry predominantly within the memory controller 401.Accordingly, in addition to a data pipe 411 for managing the flow ofread, write and configuration data between a host device 407 (e.g., oneor more processors, direct-memory-access controllers,application-specific integrated circuits, etc. coupled to the memorycontroller 401 via one or more host-access paths 402) and the memorysubsystem 403, and request logic 413 for forwarding read, write,maintenance and configuration requests to the memory subsystem 403, thememory controller is provided with adaptive timing calibration circuits417, 419 and 421 for establishing a desired phase relationship betweendata signals 410 and strobe signals received from the memory devices 405(DQ/DQS RX-ATC, 417), and between data and strobe signals 412transmitted to the memory devices 405 (DQ/DQS TX-ATC, 419) and betweenrequest signals, strobe signals and one or more clock signals (showngenerally at 414) transmitted to the memory devices (RQ/CLK TX-ATC,421), respectively.

In the embodiment of FIG. 12, data is transferred bidirectionallybetween the memory controller 401 and memory devices 405 with each setof N data links (DQxN) being associated with a mask link (DM) and a datastrobe link (DQS) to form a signaling path referred to herein as a datalane 420. In one embodiment, N is eight, thereby establishing byte-widedata lanes or byte lanes, though more or fewer data links may beprovided per data lane 420 in alternative embodiments. The data strobelink is used to convey a strobe signal that is output from thetransmitting device (i.e., memory controller 401 or one of memorydevices 405) synchronously with respect to data and mask signals outputon the corresponding data links and mask link and thus provides asource-synchronous timing reference for sampling the data and masksignals. The mask link may be used to convey masking information duringdata write operations (i.e., a mask bit that indicates whether thecorresponding data byte is to be written) or may be used to conveyadditional data information or error checking information such as aparity bit or portion of an error correction code. Similarly, duringread operations, the mask link may be used to convey read maskinginformation to the memory controller 401 (i.e., indicating whether thecorresponding read data byte is valid) or an additional read bit orerror checking information. In one embodiment, data and mask signals areoutput in response to both rising and falling edges of a timingreference to establish double data rate transmission (i.e., two symbolstransmitted per link per cycle of the timing reference). In alternativeembodiments, more or fewer symbols may be transmitted per cycle of thetiming reference to effect higher or lower data rates.

Although each of k data lanes 420 ₀-420 _(k-1) is depicted as coupledbetween the memory controller 401 and a given memory device 405 of thememory subsystem, the data lanes 420 may alternatively be allocated insubsets to respective memory devices 405 according to the width of thememory device data interfaces. For example, in a memory system havingeight byte-wide data lanes (i.e., 128 bit data path+8 bit mask path) andpopulated with memory devices each having a 32-bit wide data interface,four memory devices may be coupled to respective groups of four of thedata lanes and thus establish a rank of memory devices that is accessedas a unit (i.e., all memory devices in the rank are enabled toparticipate in a given memory read or write transaction). In such anembodiment, the memory devices may be disposed, for example, on memorymodule (e.g., a dual in-line memory module (DIMM) or single in-linememory module (SIMM)) together with a serial presence detect (SPD)storage device or other non-volatile storage device that indicates thestorage capacity and operational capabilities of the memory devices. Forexample, the non-volatile storage device may indicate whether the memorydevices include oversampling circuitry for gathering phase errorinformation that may be used for adaptive timing calibration.Accordingly, the memory controller may read the non-volatile storagedevice to determine whether the memory subsystem or some subset of thememory devices therein include circuitry to support adaptive timingcalibration and, if so, operate the memory system in an adaptive timingcalibration mode instead of a conventional operating mode. Inalternative embodiments, the memory devices and/or non-volatile storagemay be disposed on the same circuit board as the memory controller orintegrated into a multi-chip module along with the memory controller 401and/or host device 407 to form, for example, a system-in-package (SIP)DRAM system. Also, multiple ranks of memory devices may be coupled tothe data lanes in a bussed, multi-drop configuration (i.e., each datalane or any subset thereof coupled to more than one memory device), oradditional data lanes (not shown in FIG. 12) may be provided to enablepoint-to-point coupling of the memory controller to multiple ranks ofmemory devices. The data lanes 420, request path 422, clock line 424and/or backchannel 426 coupled between the memory devices 405 (or memorymodules) and the memory controller 401 may be implemented by virtuallyany signaling channel, including an electronic signal conduction path,optical signal conduction path or wireless signaling channel. Further,the host device 407, memory controller 401, and/or one or more of memorydevices 405 may be combined on a single integrated circuit die in analternative embodiment.

In the embodiment of FIG. 12, memory requests, including memory read andwrite requests (collectively referred to herein as memory accessrequests) and configuration requests, are transmitted to the memorysubsystem 403 via an M-bit request path 422 (RQ) in synchronism with amaster clock signal (Clk) transmitted on clock line 424. The masterclock signal may be generated within the memory controller 401 orelsewhere within the host system (i.e., the larger system in which thememory system 400 is a component). In one embodiment, the request path422 is coupled in parallel to each of the memory devices 405 within thememory subsystem 403 and selected subsets of the memory devices 405(e.g., ranks of memory devices) are enabled to receive and/or respond toa given memory request through a chip-select protocol (e.g., chip-selectline coupled to an address-specified rank of memory devices 405 isasserted while chip-select lines for all other memory devices 405 remainlow), request protocol (e.g., requests transmitted via path 422 includeID of memory device(s) or memory rank that is to respond to a givenmemory request) or any other device selection mechanism. Though shown asa unidirectional signaling path, the request path 422 may alternativelybe a bidirectional path, for example, to enable request, status orcontrol information to be conveyed from the memory subsystem 403 to thememory controller 401.

In the embodiment of FIG. 12, each of the memory devices 405 includes aninput/output (I/O) interface 431, access control circuitry 433, and oneor more storage arrays or storage banks 435. The I/O interface 431 isprovided to sample (capture) incoming requests and write data (orconfiguration data) in response to the master clock signal and datastrobe signals, respectively, and to output read data (or statusinformation) to the memory controller along with corresponding datastrobe signals. As discussed in further detail below, timing errordetection circuitry is provided within the I/O circuitry to oversamplethe incoming data and request signals and thereby generate phase errorinformation that may be returned to the memory controller viabackchannel communication. The backchannel may be implemented by adedicated signaling path 426 (e.g., a serial I/O path) as shown in FIG.12, or by unused bandwidth within one or more of the request path 422and data lanes 420. For example, the phase error information may betime-multiplexed onto the data lanes 420 and/or request path 422.

Still referring to memory devices 405, the access control circuitry 433responds to incoming memory access and configuration requests byenabling selected logic circuits to carry out the requested operation.In a dynamic random access memory (DRAM) embodiment, for example (i.e.,storage array(s) implemented by DRAM cells), the access controlcircuitry 433 may include row-decode circuitry for carrying out rowactivation operations and precharge operations in an address-selectedrow and storage bank, as well as column-decode circuitry for carryingout column access operations in an activated row. The access controlcircuitry 433 may additionally include read and write data pipes toenable pipelined read and write transactions within the memory device(i.e., access to an activated row, while data for a preceding orfollowing transaction is output from the read data pipe or loaded intothe write data pipe), as well as configuration circuitry for configuringthe operation of the memory device 405, including one or more one-timeor run-time programmable registers for establishing adaptive timingcalibration parameters including, for example and without limitation, asthe integration time 158, delay adjust offset 162, error validitythreshold 248 described above in reference to FIG. 10 and otherembodiments, and more generally to allow any aspect of memory deviceoperation that may need to be adjusted in response to run-time operatingconditions or application needs to be programmed in response toconfiguration commands from the memory controller or other controldevice.

Embodiments of adaptive timing calibration circuitry implemented withinthe memory controller 401 and memory devices 405 of FIG. 12 aredescribed in greater detail below in the context of a more particularmemory system. It should be understood in all such cases, thatparticular details such as number of data lines per data lane,distribution of adaptive calibration circuitry between memory controllerand memory device, and the selection of phase alignments between signalsor sets of signals may be varied according to application needs. Also,while the adaptive timing calibration circuitry is described inreference to a memory system, the adaptive timing calibration circuitry,including the circuitry and techniques described above, may be appliedin other signaling systems, including master/slave signaling systems orany other system where adaptive calibration of phase offsets betweenrelated signals may be useful.

FIG. 13 illustrates an exemplary embodiment of the data-strobe receiveinterface with adaptive timing calibration circuitry (DQ/DQS RX-ATC 417)within the memory controller of FIG. 12 and its interconnection to amemory device 405. As shown, the data lanes 420 ₀-420 _(k-1) are coupledto respective byte receivers 450 ₀-450 _(k-1). The data lanes aredepicted as byte lanes in this example, and each include eight datalines and a data mask line (collectively 446) to convey data signals,DQx8, and data mask signal, DM, and a corresponding strobe line 448 toconvey strobe signal, DQS. As shown in the exemplary expanded view ofbyte receiver 450 ₀, each of the byte receivers 450 ₀-450 _(k-1)includes a strobe enable circuit 451 and data/strobe receiver 455themselves shown, for example, in detail views 470 and 456,respectively. Referring first to detail view 456, the data/strobereceiver 455 includes a strobe delay circuit 457, a set of data delaycircuits 459 (one for each of the incoming data signals and for theincoming mask signal), data capture and timing error detection circuit461, and adaptive timing control circuit 463 each of which operategenerally as described in reference to FIG. 10 to delay the incomingstrobe signal 454 (DQS_clean) to yield a delayed strobe signal (i.e.,sample signal 460) that is aligned with the latest of the data signalsand mask signal 446, and then to delay the data signals and mask signalas necessary to achieve alignment between delayed versions of thosesignals, DQ_del 447, and the delayed strobe signal. More specifically,the data capture and timing error detection circuit 461 oversamples theincoming data and mask signals 446 to generate a phase error signal 462,and adaptive timing control circuit 463 responds to the phase errorsignal 462 by adaptively updating a strobe delay control value(DQS_RX_DVal 464) and a set of data delay control values (DQ_RX_DVal[9]466) that are used to delay the incoming data signals and mask signalindividually.

Referring to detail view 470, the strobe enable logic is provided toconvert a three-state strobe signal 448 (i.e., a signal that starts inat mid-level parked state, then transitions between high and low statesto signal presence of valid data on the corresponding data and masklines) to a clean binary strobe signal 454 (DQS_clean). In theembodiment of FIG. 13, the nominal time at which the incoming strobesignal 448 transitions from the parked state to a high or low state isdeterministic with respect to a memory request issued by the memorycontroller. That is, due to the synchronous operation of the memorydevices with respect to requests issued by the memory controller, thememory controller may expect to receive a responsive transmission apredetermined number of cycles of an internal logic clock signal 472(PClk) after transmission of a corresponding request. Thus, the memorycontroller may, at least in theory, assert a read-enable signal 474(REN) after the predetermined number of PClk cycles have transpired toenable the incoming strobe signal transitions to pass through the strobeenable logic 451 and be output in the DQS_clean signal 454 (i.e., theread-enable signal 474 acts as a gating signal, selectively enabling theincoming strobe signal 448 to be passed by strobe gating circuit 477 asthe DQS_clean signal 454). One complication in this operation is thatthe timing of the strobe signal preamble (i.e., the time between thestrobe signal transition from the parked state to the firstdata-indicating strobe signal transition) relative to the logic clocksignal 472 may drift considerably over time due to voltage andtemperature variations. Consequently, merely asserting the read-enablesignal 474 in synchrony with the logic clock signal 472 (i.e., after thepredetermined number of PClk cycles have transpired) is generallyinsufficient, as the phase offset between the logic clock signal 472 andthe desired enable point within the strobe signal preamble may result inassertion of the read-enable signal 474 too near the start or end of thestrobe signal preamble and, consequently, a spurious transition (i.e.,glitch) or missed transition in the DQS_clean signal 454, either ofwhich may result in data reception failure.

In one embodiment, an initialization-time calibration operation isperformed to compensate for phase offset between the logic clock signal472 and the desired enable point in the incoming strobe signal preamble.More specifically, the read-enable signal 474 is stepped (swept) througha range of phase delays to identify maximum and minimum phase delaysthat bound the range of error-free operation (i.e., phase delays beyondwhich glitches or missed transitions occur), and then positioned at amid-point between the maximum and minimum phase delays. Unfortunately,this approach, while acceptable in some applications, suffers from thesame susceptibility to drift-induced failure as other static calibrationoperations. That is, as with one-time calibration of strobe signaldelays, temperature and voltage drift may shift the ideal read-enablesetpoint over time, reducing timing margins and increasing thelikelihood of signaling errors.

In the embodiment of FIG. 13, the phase delay of the read-enable signal474 is adaptively calibrated to maintain a desired read-enable timingover changes in temperature and voltage and to compensate for anysystematic phase offset between logic clock signal 472 and the strobesignal preamble. More specifically, logic clock signal 472 propagatesthrough a clock delay circuit 473 to generate a delayed logic clocksignal 474 which is applied, in turn, to oversample the DQS_clean signal454 in strobe timing error detection circuit 479. Through thisoversampling operation, phase error information is obtained and passedas error signal 480 to adaptive timing control circuit 481 whichadaptively updates a delay control value 482 (DQS_en DVal) used tocontrol the propagation delay through the clock delay circuit 473.Through this closed-loop arrangement, the delayed logic clock signal 474is adaptively shifted into (and thereafter maintained in) alignment witha midpoint of the strobe signal preamble (i.e., nominally midway betweenthe strobe signal transition from parked to high or low state and thefirst data-indicating transition of the strobe signal). Further, thedelay control value 482 is additionally supplied to a read-enable delaycircuit 475 to delay the read-enable signal 474 (REN). In oneembodiment, the read-enable signal 474 is initially synchronized withthe logic clock signal 472 so that, by delaying the read-enable signal474 and logic clock signal 472 by the same propagation delay, theread-enable signal is also aligned with a midpoint (or at least adesired enable point) of the strobe signal preamble. Because the delaycontrol value 482 is adaptively updated during run-time operation, theread-enable signal is adaptively shifted to and maintained in a desiredphase relationship with respect to the strobe signal preamble despitesystematic phase offset (i.e., static phase offset) between the logicclock signal 472 and strobe signal preamble or gradual phase changesbetween the logic clock signal 472 and strobe signal preamble that mightotherwise develop due to temperature or voltage drift, or other sourcesof dynamic phase error. A more detailed circuit embodiment foradaptively adjusting the phase of the strobe-enable signal is describedbelow in reference to FIG. 19.

FIG. 14 illustrates a distribution of adaptive timing calibrationcircuitry between the memory controller 401 and a memory device 405 ofFIG. 12 to support adaptive timing calibration of the clock, data andrequest signals transmitted from the memory controller to the memorydevice. Overall, the distributed adaptive timing circuitry operates ingenerally the manner described in reference to FIG. 2, but with theerror detection circuitry and adaptive timing control circuitry splitbetween the memory device 405 and memory controller 401, respectively.Thus, each of the byte lanes 420 ₀-420 _(k-1) is coupled to a respectiveoversampling data receiver 531 ₀-531 _(k-1) (i.e., each having datacapture and timing error detection circuit functions) within the memorydevice 405 and is driven, within the memory controller 401, by arespective phase-compensating transmitter 503 ₀-503 _(k-1) (DTx) thatdelays transmission of the data, mask and strobe signals in accordancewith respective delay values Tx0_DVal[9:0]-Tx(k−1)[9:0] provided byadaptive timing control circuit 501.

Starting with the memory device side of the adaptive calibrationcircuitry, each oversampling data receiver samples signals conveyed on arespective data and mask line set (446) in response to a strobe signalconveyed on the corresponding strobe line 448 and a quadrature-delayedversion of the strobe signal to recover a respective data byte and maskbit (WData, M) and to generate phase error information for each of theconstituent data signals and mask signal. In one embodiment, the phaseerror information includes a set of valid/sign bit pairs (e.g., 9 bitpairs, including 8 for the individual data signals and one for the masksignal) designated Bi_VS in FIG. 14, where i is the byte lane index, 0to k−1. Alternatively, the valid bits may be ANDed together to form acomposite valid bit and/or the sign bits may be combined in a majoritydetector circuit as described in reference to FIG. 9, to generate acomposite sign bit. In either case, the error information for each bytelane 420 ₀-420 _(k-1) is supplied to a serial I/O controller 530 whichforwards the error information to the memory controller via back channel426. A counterpart serial I/O controller 505 within the memorycontroller 401 receives the error information from the back channel andforwards the constituent phase error indications to the adaptive timingcontrol circuit 501 which operates generally as described in referenceto FIG. 10 to update, serially or in parallel, the delay control valuesTX0_Dval[9:0]-TX(k−1)_DVal[9:0] supplied to respective strobe delaycircuits and sets of data delay circuits within each of thephase-compensating transmit circuits 503 ₀-503 _(k-1). The adaptivetiming control circuit 501 also outputs a data update signal (dUpdate)to the serial I/O controller 505 at the conclusion of each integrationperiod. The serial I/O controller forwards the data update signal to thememory device where it is received by the serial I/O controller 530 andoutput as a data-update signal 532 to the oversampling data receivers531. As discussed below, the data receivers 531 respond to thedata-update signal 532 by updating their respective sets of phase errorlogic circuits, including latching updated phase error indications andresetting error counters therein.

Still referring to FIG. 14, the memory device 405 also includes anoversampling request receiver 535 having timing error detectioncircuitry to detect clock-to-DQS and clock-to-request timing errors.More specifically, the oversampling request receiver 535 samples theincoming request signals in response to the incoming master clock signal(Clk) and a quadrature-delayed version of the clock signal (i.e.,Clk+90°) to recover requests that are forwarded to the access controlcircuitry and to generate clock-to-request phase error signals thatindicate whether the clock signal leads or lags a desired samplinginstant for the request signals. The oversampling request receiver 535also samples timing signals exported from the oversampling datareceivers 531 ₀-531 _(k-1) (i.e., cleaned versions of the strobe signalsapplied within the oversampling data receivers 531, designated assampling signals, sample0-samplek−1, in FIG. 14) in response to themaster clock signal and quadrature-delayed master clock signal togenerates clock-to-strobe phase error signals that indicate, for each ofthe data receiver sampling signals, whether the sampling signal leads orlags the clock signal. Further, in one embodiment, the timing errordetection circuitry of the oversampling request receiver 535 includeslogic to combine the error indications for the clock-to-request phaseerrors and the clock-to-strobe phase errors to yield a composite errorphase indication that corresponds to the latest of the request andstrobe signals. The clock-to-request phase error information,clock-to-strobe phase error information and composite phase errorinformation is collectively referred to herein as the clock-based timingerror information and is output from the oversampling request receiver535 to the serial I/O controller 530 in the form of a set of valid/signbit pairs designated CK/RQ/DQS_VS in FIG. 14. The clock-based timingerror information is forwarded to the memory controller 401 via backchannel 426 where it is received by counterpart serial I/O controller505. The clock-to-strobe phase error information (DQS_VS) within theclock-based timing error information is supplied to adaptive timingcontroller 501 and applied to adjust the phase of the strobe signals.The composite phase error information (CK_VS) and clock-to-request phaseerror information (RQ_VS) is supplied to an adaptive timing controller507 for the request and clock signals which, in response, generatesupdated delay control values, RQ_DVal[M−1:0] and CK_DVal, that aresupplied to a phase-compensating request transmitter 509 (RTx) to adjustthe phases of the transmitted clock and request signals.

FIG. 15 illustrates an embodiment of an oversampling data receiver 550that may be used to implement each of the oversampling data receivers531 ₀-531 _(k-1) of FIG. 14. As shown, the oversampling data receiver550 includes a data strobe receiver 125, data slice receivers 551 ₀-551₇ and a quadrature delay element 137, divider circuit 263 and clockdrivers 321, 323 and 325 to provide a sampling signal 328 (sample),quadrature sampling signal 330 (qsample) and subrate sampling signal 332(sdiv) to each of data slice receivers 551 ₀-551 ₇ as generallydescribed in reference to FIG. 10, with each of the data slice receivers551 ₀-551 ₇ including an input amplifier, data and edge samplingcircuits 133 and 135, error logic gates 145 and 147 and subrate phaseerror logic 335 that operate as described above to collectively recovera sequence of even and odd data bytes (Even[7:0] and Odd[7:0]) andcorresponding phase error information, VS[7:0][1:0] from data signalsreceived via nodes 103 ₀-103 ₇. Note that the data strobe receiver 125within the memory device 405 may be simplified relative to thecounterpart data strobe receiver 125 within the memory controller, asthe timing of the strobe enable signal may be enforced by establishing afixed phase relationship between the master clock signal and theincoming data strobe signal. The oversampling data receiver 550 furtherincludes a data mask receiver 551 ₈ (DM Rcvr) which operates ingenerally the same manner as the data slice receivers 551 ₀-551 ₇ torecover a sequence of even and odd data mask bits that correspond to theeven and odd data bytes. As shown, a data-update signal 532 (dUpdate)from the serial I/O controller is provided to the update inputs of eachof the data slice receivers 531 ₀-531 ₇ and the data mask receiver 531 ₈and, when asserted, initiates an update operation within each receiver531 to enable an updated valid/sign bit pair (i.e., phase error signal)to be latched or registered at the receiver output and to clear theinternal error counters.

In one embodiment, the nine valid/sign bit pairs from data slicereceivers 531 ₀-531 ₇ and the data mask receiver 531 ₈ are output to theserial I/O controller in parallel as byte-lane error information 565(B0_VS[9:0]), thus permitting the corresponding delay control valuesmaintained within the memory controller to be updated concurrently. Toreduce consumption of backchannel bandwidth, the valid bits may belogically ANDed as performed by optional logic AND gate 563 to form acomposite valid bit 564 that is used to qualify each of the sign bits.Also, instead of updating each of the data slice receivers 531 ₀-531 ₇and the data mask receiver 531 ₈ simultaneously, the receivers 531 maybe updated in round-robin fashion as described in reference to FIG. 10,with the error indications from each of the receivers 531 forwarded tothe serial I/O controller via a multiplexed path rather than inparallel. Further, as shown at 560, instead of returning individualerror sign bits to the memory controller as in embodiment 561, majoritydetection logic 566 may be provided to generate a composite sign bit 567(i.e., as described in reference to FIG. 9) to be paired with compositevalid bit 564 generated by logic AND gate 563 and thus form a two-bitbyte-lane error value 568 (B0_VS[1:0]). In such an embodiment, the datastrobe signal may be delayed within the memory controller to align thecorresponding sampling signal 328 within each oversampling data receiver550 of the memory device with the median of the desired samplinginstants for the data slice receivers 551 ₀-551 ₇ and mask signalreceiver 551 ₈.

FIG. 16 illustrates an embodiment of an oversampling request receiver600 that may be used to implement the oversampling request receiver 535of FIG. 14. As shown, the oversampling request receiver includes a clockreception and distribution circuit 606, a set of M request signalreceivers 623 ₀-623 _(M-1) (R0 Rcvr-R(M−1) Rcvr), a set of kclock/strobe phase comparators 651 ₀-651 _(k-1) and compositing logic670. The clock distribution circuit 606 includes an input amplifier 607coupled to a clock input node 601 to receive the incoming master clocksignal, Clk, and a quadrature delay element 609, divider circuit 611 andclock drivers 613, 615, 617 that operate to deliver a clock signal 614(clk), quadrature clock signal 616 (qclk) and subrate clock signal 618(clkdiv) to the request signal receivers 623 and clock/strobe phasecomparators 651.

Each of the request signal receivers 623 ₀-623 _(M-1) is coupled toreceive a request signal (RQ[0]-RQ[M−1]) from is respective one ofrequest input nodes 603 ₀-603 _(M-1) and is implemented in generally thesame manner as the data signal receivers described in reference to FIG.15. Thus, as shown in the detail view of request signal receiver 623 ₀,each request signal receiver includes an input amplifier 625 to forwardthe request signal from the request input node 603, request samplingcircuit 627 to sample the incoming request signal in response to risingand falling edges of the clock signal 614 (or in response to risingedges of respective complementary components of clock signal 614 as in adifferential clock arrangement), and an edge sampling circuit 629 tosample transitions in the incoming request signal in response toquadrature clock signal 616. The request samples generated within the Mrequest signal receivers are output from the oversampling requestreceiver 600 as a sequence of even and odd request values, 642 a and 642b. Each request value may itself constitute a memory access request (orconfiguration request or request for status) or may be combined withother request values to form a complete request, the latter arrangementallowing for transmission of packetized requests.

Within a given request signal receiver 623, each set of even and oddrequest samples and the intervening edge sample is provided, as atri-sample, to error logic circuits 639 and 641 which generate positiveand negative error signals, pErr and nErr, as described above. Thepositive and negative error signals are supplied to subrate phase errorlogic circuit 335 which also operates as described above in reference toFIGS. 7, 9 and 10 to accumulate the positive and negative errorindications over time to produce an integrated, differential phaseerror. In the embodiment of FIG. 16, an updated phase error is latchedat the valid/sign output of the subrate phase error logic circuit 335 atthe conclusion of each integration period (marked by assertion of therequest-update signal 536 (rUpdate) at the update input of each requestsignal receiver 623) as a valid bit and error sign bit (valid/sign) thatindicate, respectively, whether a threshold number of phase errors havebeen detected during the integration period and whether more positive ornegative phase errors were detected.

Each of the clock/strobe phase comparators 651 ₀-651 _(k-1) receives theclock signal 614, quadrature clock signal 616, subrate clock signal 618,and a respective one of sampling signals 540 ₀-540 _(k-1) (i.e., strobesignals) exported from the oversampling data receivers as shown in FIG.14. Referring to the detail view of clock/strobe comparator 651 ₀, theincoming sampling signal 540 ₀ (sample0) is provided to data and edgesampling circuits 653 and 655 which are clocked by the quadrature clocksignal 616 and clock signal 655, respectively. By this arrangement, theclock signal 614, which is nominally aligned with strobe signaltransitions, is used to capture edge samples of the sampling signal 540₀, while the quadrature clock signal 616 is used to capture data-levelsamples (i.e., analogous to data samples) of the sampling signal 540 ₀.Error logic gates 659 and 661 are provided to compare the edge anddata-level samples of each successive tri-sample and thus providepositive and negative-error signals to a subrate phase error logiccircuit 335 to indicate whether transitions of clock signal 614 occurlate or early relative to transitions of sampling signal 540 ₀. As inthe request signal receivers, the phase error logic 335 accumulates thepositive and negative error indications over time to produce anintegrated, differential phase error, latching a correspondingvalid/sign bit pair at the valid/sign output and clearing internalcounters in response to assertion of the request-update signal 536(rUpdate).

Still referring to FIG. 16, the compositing logic 670 receives thevalid/sign bit pairs from each of the request signal receivers 623 ₀-623_(M-1) and clock/strobe phase comparators 651 ₀-651 _(k-1) and generatesa composite valid/sign bit pair by logically ANDing the valid bits inAND gate 671 and logically ORing the sign bits in OR gate 673. By thisarrangement, the composite sign bit (i.e., output of OR gate 673)corresponds to the latest of the sampling signals and request signals,and the composite valid bit indicates that the composite sign bit isvalid when all the constituent sign bits are indicated to be valid.Though not specifically shown, the valid bits for the request signalreceivers 623 may be ANDed to generate a composite valid bit for the setof request sign bits (e.g., to conserve backchannel bandwidth) and/ormajority logic may be provided to generate a composite sign bit for therequest signal receivers that represents a majority vote as to whetherto advance or retard the phase of the request signals (or the clocksignal) to achieve phase alignment between the request and clocksignals. Similarly, the valid bits from the clock/strobe phasecomparators 651 may be ANDed to generate a composite valid bit for theset of clock/phase sign bits and/or majority logic may be provided togenerate a composite sign bit for the clock/strobe phase comparators651.

FIG. 17A illustrates an exemplary embodiment of a phase-compensatingdata/strobe transmitter 700 that may be used to implement each of thephase-compensating transmitters 503 ₀-503 _(k-1) of FIG. 14. As shown,the transmitter 700 receives data byte TxData[7]-TxData[0] and mask bitTxDM as data inputs, a transmit strobe signal, TDQS, as a strobe signalinput and transmit delay control values Tx_DVal[9:0] as delay controlvalues for each of ten signals to be transmitted. The transmitter 700includes respective delay lines 701 and 703 ₀-703 ₈ to delay each of theinput signals in accordance with a corresponding one of the ten delaycontrol values. That is, the propagation delay through a respective oneof delay lines 703 ₀-703 ₇ is selected for each of the input datasignals by a corresponding one of delay control valuesTx_DQ_DVal[0]-Tx_DQ_DVal[7], the propagation delay through delay line703 ₈ for the data mask signal is selected according to delay controlvalue Tx_DM_DVal and the propagation delay through the delay line 701for the data strobe signal is selected according to delay control valueTx_DQS_DVal. By this operation, the phase of each of the signalstransmitted in a given byte lane may be individually adjusted accordingto phase error information returned from the recipient memory device. Asshown, the delayed data and mask signals are output from the memorycontroller via nodes 103 ₀-103 ₈ by output drivers 704 ₀-704 ₈,respectively. The delayed strobe signal is likewise output from thememory controller via node 101 by output driver 702.

FIG. 17B illustrates an exemplary embodiment of a phase-compensatingrequest/clock transmitter 708 that may be used to implement thephase-adjusting request transmitter 509 of FIG. 14. As shown,transmitter 708 receives an M-bit request value Req[M−1:0] as a requestinput, the memory controller logic clock signal, PClk, as a clock input,and request/clock delay control values Req/Ck_DVal[M:0] as delay controlvalues for each of M+1 signals to be transmitted. The transmitter 708includes respective delay lines 709 and 711 ₀-711 _(M-1) to delay eachof the input signals in accordance with a corresponding one of the tendelay control values. That is, the propagation delay through arespective one of delay lines 711 ₀-711 _(M-1) is selected for each ofthe input data signals by a corresponding one of delay control valuesRQ_DVal[0]-RQ_DVal[M−1] and the propagation delay through the delay linefor the master clock signal is selected according to delay control valueCk_DVal. By this operation, the phase of the master clock signal and thephase of each of the signals transmitted via a given request signal linemay be individually adjusted according to phase error informationreturned from the recipient memory device. As shown, the delayed requestsignals are output from the memory controller via nodes 603 ₀-603 _(M-1)by output drivers 712 ₀-712 _(M-1), respectively, and the master clocksignal is output via node 601 by output driver 710.

FIG. 18 illustrates an exemplary adaptive calibration sequence that maybe applied within the memory system of FIG. 13 to establish a desiredphase alignment between signals transmitted from the memory controller401 to the memory devices 405. At 741, the clock delay is initialized to+45° (halfway to the nominal target of 90°), all data (DQ) and request(RQ) delays are initialized to +10° to provide headroom for phaseadvancement, and all strobe (DQS) delays are initialized to +100°, thenominal quadrature sampling point for the delayed-by-10° data signals.At 743, the master clock signal delay is adaptively adjusted to alignthe master clock signal with the latest of the request signals andstrobe signals, and thus is shifted toward the +90° point for quadraturealignment with the request signals and edge alignment with the strobesignals. Referring to FIGS. 14, 16 and 17B, the memory controllerapplies the composite error indication, CK_VS (e.g., generated bycompositing logic 670 within the request oversampler 600 of FIG. 16), toupdate the clock delay control value, Ck_DVal, until the desiredalignment between the master clock signal (Clk) and latest of therequest signals and data strobe signals is achieved. After the masterclock signal has reached the desired alignment (e.g., determined bydithering of the composite error indication, CK_VS, adaptation of themaster clock signal phase is halted or otherwise disabled as shown at745, and adaptation of the phases of the request signals, strobe signalsand data signals is commenced. More specifically, as shown at 747, eachof the request signal delays and strobe signal delays are adaptivelyadjusted to achieve quadrature alignment between the request signals andthe master clock signals and to achieve edge-alignment between thestrobe signals and the master clock signal. Also, as shown at 749, eachof the data signal delays is adaptively adjusted to achieve quadraturealignment between the sampling signal (i.e., delayed strobe signal) fora given byte lane and the corresponding the mask and data signals. Bycontinuing to adaptively calibrate the request, strobe and data signalsthrough run-time operation of the memory system, phase differencesbetween the various signals that might otherwise develop (e.g., due totemperature or voltage drift) are compensated for, and the desired phasealignment maintained.

FIG. 19 illustrates an embodiment of a strobe enable circuit 760 thatmay be used to implement the strobe enable circuit 451 of FIG. 13. Aread-enable signal 474 (REN) is supplied from the memory controller core(e.g., from the request logic 413 shown in FIG. 12) at a time determinedaccording to an expected data transmission from the memory subsystem.The read-enable signal 474 is synchronized with logic clock signal 472(PClk) in flop-flop 761, then propagates through a variable-delaycircuit 763 (REN Delay) to yield a phase-adjusted read-enable signalreferred to herein as a strobe-enable signal 762. The logic clock signal472 also propagates through a variable-delay circuit 765 (PClk Delay) toyield a delayed logic clock signal 766, dPClk. In the embodiment of FIG.19, the strobe-enable signal 762 is synchronized with the delayed logicclock signal 766 in flip-flop 767 to account for delay mismatch betweenthe variable-delay circuits 763 and 764, though such synchronization(and flip-flop 767) may be omitted in an alternative embodiment.

In one embodiment, the strobe-enable signal 764 is supplied to atransparent latch circuit 769 which operates by passing thestrobe-enable signal 764 to a first input of AND gate 771 (i.e., anenable gate) during the preamble phase of a strobe signal 104 (DQS)which is received via strobe input node 103 and forwarded by inputamplifier 127 to a second input of AND gate 771 and to the enable inputof transparent latch circuit 769. By this arrangement, during thepreamble phase when the strobe signal 104 transitions from a parked(i.e., mid-level state) to a low signal level, the latch circuit 769 isoperated in transparent mode (i.e., due to the logic-low signal at itslatch-enable input), passing the strobe-enable signal 764 to an input ofAND gate 771 and thus ensuring that the first rising edge of the strobesignal 104 (i.e., the first data-indicating strobe signal transition)passes through AND gate 771 to appear in DQS_clean signal 126. As thestrobe signal 104 goes high, the transparent latch transitions to alatch mode to latch the high state of the strobe-enable signal 764 untilthe next low-going edge of the strobe signal 104.

In one embodiment, each burst of data values timed by the strobe signal104 includes an even number of symbols, in which the firstdata-indicating transition is a rising edge and the finaldata-indicating transition is a falling edge. Accordingly, the strobesignal 104 will be high just before a final, low-going strobe signaltransition that corresponds to the final symbol in a burst sequence, andthus will latch a logic-high state of the strobe-enable signal 764 atthe input of AND gate 771 and ensure that the final low-going transitionof the strobe signal 104 will pass through AND gate 771 and appear inthe DQS_clean signal 126, even if the strobe-enable signal 764 isdeasserted slightly in advance of the final low-going transition ofstrobe signal 104. Note that this operation is particularly beneficialin the context of the automatic timing calibration performed by strobeenable circuit 760, which, as will be described in further detail below,operates to center the strobe-enable signal 764 between the start andend of the strobe signal preamble, and thus, because timed by thedelayed logic clock signal 766, will be deasserted at a time that issubstantially edge-aligned with the final low-going edge of the strobesignal 104. That is, in one embodiment, the strobe signal preamble is alogic clock cycle in duration so that, when the strobe-enable signal 764is centered midway between the start and end of the strobe signalpreamble, the strobe-enable signal 764 will be deasserted in a time bandcentered about the final low-going edge of the strobe signal 104, andpotentially just slightly before the final low-going edge of the strobesignal 104. By latching the high state of the strobe-enable signal 764at the input of AND gate 771 in advance of the final low-going edge ofthe strobe signal 104, the final low-going edge of the strobe signal 104is ensured to pass through AND gate 771 and appear in the DQS_cleansignal, even if the strobe-enable signal 764 is deasserted slightlyprematurely.

Still referring to FIG. 19, the clean strobe signal 126 (DQS_clean) anddelayed logic clock signal 766 are supplied to a timing error detectioncircuit 780 (also referred to herein as an adaptive strobe-enablecentering loop) which samples the clean strobe signal 126 in response tothe delayed logic clock signal 766 and in response to aquadrature-delayed logic clock signal 786 (i.e., generated bypropagation of the delayed logic clock signal 766 through quadraturedelay element 788) and thus generate data-level samples and edge samplesof the clean strobe signal 126. That is, rising and falling edges of thedelayed logic clock signal 766 (or rising edges of complementarycomponents of a differential delayed clock signal 766) are applied todata-level sampling circuit 781 to generate samples of the clean strobesignal 126 on either side of a strobe signal transition (data-levelsamples 788 a, 788 b), while the quadrature-delayed logic clock signal786 (generated by quadrature delay element 785) is supplied to edgesampling circuit 783 to capture samples of the clean strobe signal 126as it transitions between upper and lower levels (i.e., edge samples790). The data-level samples 788 a/788 b and edge samples 790 areprovided as a sequence of tri-samples (i.e., successive data-levelsamples and intervening edge sample) to error logic gates 791 and 793which generate positive and negative error signals, pErr and nErr, asdescribed above in reference to FIG. 2. The positive and negative errorsignals are supplied to up/down inputs of phase error logic 795 whichoperates generally as described in reference to FIG. 6 to increase ordecrease a differential error count, at each rising edge of the delayedlogic clock signal 766, according to whether the tri-sample captured inthe preceding delayed logic clock cycle indicates that the quadraturedelayed logic clock signal 786 transitioned early (i.e., nErr) or late(pErr) relative to a transition of the clean strobe signal 126. In theembodiment of FIG. 19, the sign of the differential error countindicates whether a majority of the error indications indicate an earlyor late delayed logic clock signal 766 and is output to an adaptivetiming control circuit 233 as an error sign value (Sign). The phaseerror logic 795 also includes circuitry to compare the total number ofpErr and nErr assertions during a given integration period with a fixedor programmable threshold and to generate, according to the comparisonresult, a valid signal (Valid) which qualifies or disqualifies thecorresponding error sign as described above. While not specificallyshown, the phase error logic 795 may include additional circuitry toenable subrate loop operation as described in reference to FIG. 7.

The adaptive timing control circuit 233 includes an integration timer153, delay control storage element 155 and delay value update circuit237 (itself including multiplexers 157 and 239, and arithmetic operators159 and 161) that operate generally as described in reference to FIG. 6to increment, decrement or maintain without change the active delaycontrol value 482 (DVal) at the conclusion of each integration period(signaled by update signal 154), thus producing an updated delay controlvalue 796 (DVal′). As in the embodiment of FIG. 6, the delay valueupdate circuit 237 outputs an updated delay control value 796 (DVal′)that is adjusted by a fixed or programmed offset value 162, (which maybe the same or different offset value than applied in like numberedreferences to the offset value 162 in embodiments described above) or,if the valid signal output from the phase error logic 795 is low, passesthe active delay control value 482 through multiplexer 796 to be theupdated delay control value 796. In any case, delay control value 796 isstored within the delay control storage element 155 at the subsequentassertion of the update signal 154, thus establishing a new (orsame-value) active delay control value 482. By this operation, anegative feedback loop is established to adaptively adjust the phasedelay of delayed clock signal 766, and therefore the strobe-enablesignal 764, to maintain edge-alignment between the quadrature delayedlogic clock signal 786 and the clean strobe signal 126. By aligning thequadrature delayed clock signal 786 and clean strobe signal 126 in thismanner, a rising edge transition of the delayed logic clock signal 766,and thus the rising edge of the strobe-enable signal 764, is ensured toprecede the first data-indicating edge of the incoming strobe signal 104by approximately 90° and thus be centered substantially midway betweenthe start and end of the strobe signal preamble. Accordingly, thestrobe-enable signal 766 will enable the incoming strobe signal 104 tobe passed as the clean strobe signal 126 at an appropriate time withinthe strobe signal preamble, regardless of phase drift between theincoming strobe signal 104 and logic clock signal 472 (PClk).

FIG. 20 illustrates a delay-locked loop circuit 815 (DLL) that may beused to generate control signals for establishing quadrature delay in aquadrature delay element 817 such as the quadrature delay elementsdiscussed in embodiments above. In one embodiment, the delay locked loopcircuit 815 includes a delay line 823 implemented by a set of fourdaisy-chained delay elements 825 ₀-825 ₃ (i.e., coupled in series,output-to-input) and a delay control circuit 821 coupled to receive areference clock signal 816 (e.g., the logic clock signal 416 generatedby clock generator 415 in the memory controller of FIG. 12, or themaster clock signal (Clk) supplied to the memory devices 405 of FIG. 12)at a non-inverting input and a feedback clock signal 826 from the delayline 823 at an inverting input. In one embodiment, the delay controlcircuit 821 includes a phase detector (not specifically shown) togenerate a logic low or high phase error signal according to whether thereference clock signal 816 leads or lags the feedback clock signal 826,and a bias control circuit (also not shown) to adjust positive-bias andnegative-bias voltages 824 (p-bias, n-bias) supplied to each of thedelay elements in response to the phase error signal. In the embodimentof FIG. 20, each of the delay elements 825 ₀-825 ₃ is formed by avariable slew-rate inverter 830 having transistors 835 and 837 coupledin an inverter configuration and slew-rate control transistors 831 and833 coupled respectively between the sources of transistors 835 and 837,and upper and lower supply voltages (e.g., VDD and ground). The gateterminals of the slew-rate control transistors 831 and 833 are coupledto receive the p-bias and n-bias signals, respectively, and thus operateto change the effective inverter supply voltage (i.e., voltagedifferential between the sources of inverter-configured transistors 835and 837). More specifically, as n-bias is raised and p-bias is lowered,the voltage drop across the slew-rate control transistors 831 and 833decreases, increasing the effective inverter supply voltage and therebyincreasing the output slew rate of the inverter 830 to reduceinput-to-output propagation delay. Conversely, when n-bias is loweredand p-bias raised, the slew-rate of the inverter 830 is decreasedthereby increasing the inverter propagation delay.

Still referring to FIG. 20, the delay control circuit 821 closes anegative feedback loop that operates to adjust the p-bias and n-biasvoltages 824 as necessary to achieve phase lock between a rising edge ofthe reference clock signal 816 and the falling edge of the delay-lineoutput (i.e., feedback clock signal 826). By this operation, a netdelay-line propagation delay of 180° is enforced by operation of thedelay locked loop 815 with each of the four delay elements 825 ₀-825 ₃contributing a 45° delay to the 180° total. Further, by exporting thep-bias and n-bias voltages 824 to series coupled pairs of 45° delayelements 825 as shown in quadrature delay circuit 817, a 90° delay maybe achieved between an input signal 818 (SIG0) and output signal 820(SIG0_90). In alternative embodiments, more or fewer delay elements 825may be provided within the delay line 823 to enable development ofp-bias and n-bias voltages 824 that establish per-delay-element delaysgreater or less than 45°. Such delay elements may be used to constructdelay circuits that exhibit more or less than 90° with such delaycircuits applied, for example, in signaling systems that operate at datarates greater than the double data rate described above, or thatotherwise have data eyes that are wider or narrower than 180° and thushave sampling points that are offset from edges of data eyes by anglesother than 90°.

FIG. 21 illustrates an embodiment of a variable delay circuit 850 thatmay be used, for example, to implement variable delay circuit 107 shownin FIGS. 1A, 2, 5, 6, 7, variable delay circuit 127 shown in FIG. 9,variable delay circuits 363 shown in FIG. 10 and the delay lines 701,703, 709 and 711 shown in FIGS. 17A and 17B. The variable delay circuit850 includes a delay locked loop 851, strobe delay line 853 a,interpolator 855 and clock tree circuit 857. The delay locked loop 851includes a delay line 853 b and delay control circuit 863 both coupledto receive a reference clock signal, RefClk, which may be, for example,the logic clock signal, PClk, when the variable delay circuit 850 isincluded within a memory controller or the master clock signal, Clk,when included within a memory device. In the particular embodimentshown, the delay line 853 b is implemented by a daisy-chained sequenceof current-starved inverter elements 830 and thus forms acurrent-starved delay line generally as described in reference to FIG.20. The delay control circuit 863 is coupled to receive the output ofthe delay line 853 b (i.e., delayed clock signal 854) and the referenceclock signal at respective phase detect inputs and includes circuitry todetect a phase difference between the clock signals and to adjust adelay control signal 864 (having component signals pbias and nbias inthis example) that, in turn, adjusts the propagation delay through theinverter elements 830 in a direction counter to the phase difference,thus effecting a negative feedback loop that operates to enforce phasealignment between the delayed clock signal 854 and the reference clocksignal. By this operation, a single-cycle delay (or half cycle delaydepending on whether the reference clock signal is inverted relative todelayed clock signal 854) is established across the delay line 853 b,with the delay through each of the component inverter elements beingsubstantially equal to the reference clock period divided by the numberof inverter elements 830. For example, as the particular embodimentshown includes eight inverter elements 830, the delay through each ofthe inverter elements 830 is approximately 45° or one-eighth of thereference clock period. More or fewer inverter elements 830 may beprovided in alternative embodiments and/or other types of delay elementsmay be used.

Still referring to FIG. 21, the delay control signal 864 is exportedfrom the delay-locked loop 851 to the strobe delay line 853 a and usedto control the propagation delay through inverter elements 830 therein.In one embodiment, the strobe delay line 853 a is implemented by thesame number of inverter elements 830 as delay line 853 b and thusexhibits substantially the same single-cycle delay in response to atransition of an input signal and additionally yields a phase-shiftedset of signal transitions that are progressively delayed, relative toone another, by a phase angle that corresponds to the reference clockperiod divided by the number of inverter elements 830 in the strobedelay line 853 a. More specifically, the first inverter element 830 inthe strobe delay line 853 a is coupled to receive a strobe signal (DQS)so that each transition of the strobe signal appears at the output ofthe final inverter element 830 of the strobe delay line 853 a onereference clock cycle later, and appears at outputs of the intermediateinverter elements 830 at phase increments of 360°/N, where N is thenumber of inverter delay elements. Thus, in the eight-element embodimentshown, each transition of the incoming strobe signal (e.g., a DQS_cleansignal) produces a set of eight strobe signal transitions having phaseoffsets that range from 45° to 360° in 45° phase steps. The 360° may beviewed as being a 0° phase angle with a one clock cycle latency, so thatthe strobe delay line is considered to yield a set of phase-shiftedstrobe signals 852 that are delayed by angles of 0°, 45°, 90°, 135°,180°, 225°, 250° and 315°. The phase-shifted strobe signals 852 aresupplied to the interpolator 855 which includes logic to select a pairof the phase-shifted strobe signals according to vector-select componentof a delay control value, DVal, and to interpolate between the selectedpair of phase-shifted strobe signals 852 according to an interpolationcomponent of the delay control value to generate phase-delayed strobesignal 856. As an example, in one embodiment, the delay control value isa nine-bit value in which the most significant three bits constitute thevector-select component (thus enabling selection of one of eightpossible pairs of the phase-shifted strobe signals 852 boundingrespective phase ranges 0-45°, 45-90°, 90-135°, 135-180°, 180-225°,225-270°, 270-315° and 315-0°), and the least significant six bitsconstitute the interpolation component, thus enabling 64 interpolationsteps between the selected pair of phase-shifted strobe signals. By thisarrangement as the count value is incremented from 0 to a maximum value,the phase delay of the phase-delayed strobe signal is stepped from 0°(DVal=0 0000 0000b, where ‘b’ designates binary notation) to 359.3°(DVal=1 1111 1111b) in approximately 0.7° increments (i.e., 360/2⁹).More or fewer bits may be provided within the interpolation component ofthe delay control value in alternative embodiments with resultingincrease or decrease in phase-step resolution. Also, fewer vector-selectbits may be provided where fewer than eight pairs of phase-shifted delaysignals are to be selected. For example, while a full 360° range ofphase delays is provided by the delay control circuit 850, one or moreinverter elements 830 may be omitted from strobe delay line 853 a withcorresponding reduction of interpolator circuitry and vector-select bitswithin the delay control value to implement a variable delay circuithaving a phase range of less than 360°.

Still referring to FIG. 21, the phase delayed strobe signal 856 issupplied to the clock tree circuit 857 as shown, which operates togenerate a number of instances of a delayed strobe signal, DQS_DEL,according to the desired signal fan-out. In an embodiment having asufficiently low fan-out requirement for the delayed strobe signal, theclock tree circuit may be omitted and the phase-delayed strobe signal856 itself applied as the delayed strobe signal.

Reflecting on the adaptive timing calibration operations discussedabove, it can be seen that the phase updates carried out to compensatefor phase drift between an incoming timing signal and a desired samplinginstant are triggered by transitions in the incoming data signal.Consequently, during extended idle periods in which the incoming datasignal does not transition (and thus the corresponding timing signal, ifa strobe signal, also does not transition) or does not containsufficient transition density, timing updates may not be performed, thusrendering the signaling system susceptible to gradual phase drift. Inone embodiment, this circumstance is avoided by encoding outgoing datatransmissions so that all possible data patterns to be transmittedinclude a number of transitions sufficient to support substantiallycontinuous adaptive timing calibration. For example, in one embodiment,an 8-bit-to-10-bit encoder is provided to encode each 8-bit sequence tobe transmitted on a given data line (or request line) into a 10-bitsequence having a desired number of data state transitions. After signalreception, the received 10-bit sequence may be decoded to restore theoriginal 8-bit sequence. In an alternative embodiment, one or more ofthe devices in the signaling system (e.g., a master device in amaster-slave signaling system, or all the devices or a designated one ofthe devices in a peer-to-peer signaling system) may monitor signaltransmission on the data lines and issue occasional calibrationtransmissions as necessary to maintain an overall transition densitythat is sufficient to support a desired adaptive timing calibration rateand thus avoid undue phase drift. As a specific example, a memorycontroller within a memory system may detect a paucity of memory accessrequests from a host device (or a selection of a particular operatingmode, such as a low power mode in which data transmission and receptionis limited or temporarily suspended) and, in response, enter aself-directed mode in which the memory controller itself initiatesperiodic or occasional read and write operations (i.e., dummy reads andwrites) within the memory subsystem to ensure sufficient transitiondensity for adaptive timing calibration operations. In one embodiment,for example, the memory controller may select one or more unused storagelocations within the memory subsystem (or one or more predeterminedand/or programmably selected storage locations that are reserved fordummy read and write operations) and issue periodic write and readinstructions directed to such storage locations. Alternatively, thememory controller may issue reads and writes to another resource withinthe memory device (e.g., a status register or even a non-existentlocation indicated by a particular out-of-bound or otherwisespecially-coded address value or request code). Further any such readand write operations may be hidden under one or more other maintenanceoperations (i.e. performed concurrently therewith to reduce impact onmemory subsystem availability) including, for example and withoutlimitation, refresh operations, signal driver calibration operations,equalization calibration operations, and so forth.

It should be noted that the various circuits disclosed herein may bedescribed using computer aided design tools and expressed (orrepresented), as data and/or instructions embodied in variouscomputer-readable media, in terms of their behavioral, registertransfer, logic component, transistor, layout geometries, and/or othercharacteristics. Formats of files and other objects in which suchcircuit expressions may be implemented include, but are not limited to,formats supporting behavioral languages such as C, Verilog, and HLDL,formats supporting register level description languages like RTL, andformats supporting geometry description languages such as GDSII, GDSIII,GDSIV, CIF, MEBES and any other suitable formats and languages.Computer-readable media in which such formatted data and/or instructionsmay be embodied include, but are not limited to, non-volatile storagemedia in various forms (e.g., optical, magnetic or semiconductor storagemedia) and carrier waves that may be used to transfer such formatteddata and/or instructions through wireless, optical, or wired signalingmedia or any combination thereof. Examples of transfers of suchformatted data and/or instructions by carrier waves include, but are notlimited to, transfers (uploads, downloads, e-mail, etc.) over theInternet and/or other computer networks via one or more data transferprotocols (e.g., HTTP, FTP, SMTP, etc.).

When received within a computer system via one or more computer-readablemedia, such data and/or instruction-based expressions of the abovedescribed circuits may be processed by a processing entity (e.g., one ormore processors) within the computer system in conjunction withexecution of one or more other computer programs including, withoutlimitation, net-list generation programs, place and route programs andthe like, to generate a representation or image of a physicalmanifestation of such circuits. Such representation or image maythereafter be used in device fabrication, for example, by enablinggeneration of one or more masks that are used to form various componentsof the circuits in a device fabrication process.

In the foregoing description and in the accompanying drawings, specificterminology and drawing symbols have been set forth to provide athorough understanding of the present invention. In some instances, theterminology and symbols may imply specific details that are not requiredto practice the invention. For example, the interconnection betweencircuit elements or circuit blocks may be shown or described asmulti-conductor or single conductor signal lines. Each of themulti-conductor signal lines may alternatively be single-conductorsignal lines, and each of the single-conductor signal lines mayalternatively be multi-conductor signal lines. Signals and signalingpaths shown or described as being single-ended may also be differential,and vice-versa. Similarly, signals described or depicted as havingactive-high or active-low logic levels may have opposite logic levels inalternative embodiments. As another example, circuits described ordepicted as including metal oxide semiconductor (MOS) transistors mayalternatively be implemented using bipolar technology or any othertechnology in which a signal-controlled current flow may be achieved.With respect to terminology, a signal is said to be “asserted” when thesignal is driven to a low or high logic state (or charged to a highlogic state or discharged to a low logic state) to indicate a particularcondition. Conversely, a signal is said to be “deasserted” to indicatethat the signal is driven (or charged or discharged) to a state otherthan the asserted state (including a high or low logic state, or thefloating state that may occur when the signal driving circuit istransitioned to a high impedance condition, such as an open drain oropen collector condition). A signal driving circuit is said to “output”a signal to a signal receiving circuit when the signal driving circuitasserts (or deasserts, if explicitly stated or indicated by context) thesignal on a signal line coupled between the signal driving and signalreceiving circuits. A signal line is said to be “activated” when asignal is asserted on the signal line, and “deactivated” when the signalis deasserted. Additionally, the prefix symbol “/” attached to signalnames indicates that the signal is an active low signal (i.e., theasserted state is a logic low state). A line over a signal name (e.g.,‘<signal name>’) is also used to indicate an active low signal. The term“coupled” is used herein to express a direct connection as well as aconnection through one or more intervening circuits or structures. Theterm “exemplary” is used to express an example, not a preference orrequirement.

Various aspects of the subject matter described herein are set forth,for example and without limitation, in the following numbered clauses:

-   1. A signaling system comprising:    -   a first integrated circuit (IC) device to receive a data signal        and a strobe signal and having circuitry to sample the data        signal at times indicated by the strobe signal to generate phase        error information and circuitry to output the phase error        information from the first IC device; and    -   a second IC device to output the data signal and the strobe        signal to the first IC device, the second IC device having delay        circuitry to generate the strobe signal by delaying an aperiodic        timing signal for a first time interval and timing control        circuitry to receive the phase error information from the first        IC device and adjust the first time interval in accordance with        the phase error information.-   2. The signaling system of clause 1 wherein the circuitry to sample    the data signal at times indicated by the strobe signal to generate    phase error information comprises:    -   a data sampling circuit to sample the data signal in response to        the strobe signal to generate a sequence of data samples; and    -   an edge sampling circuit to sample the data signal in response        to a phase-shifted version of the strobe signal to generate a        sequence of edge samples.-   3. The signaling system of clause 2 wherein the circuitry to sample    the data signal at times indicated by the strobe signal to generate    phase error information further comprises circuitry to compare each    pair of the data samples with an intervening one of the edge sample    to generate the phase error information.-   4. The signaling system of clause 1 wherein the delay circuitry    comprises an input to receive a delay control value from the timing    control circuitry, and circuitry to apply the delay control value to    establish the first time interval.-   5. The signaling system of clause 4 wherein the timing control    circuitry includes a delay control update circuit to increase or    decrease the delay control value according to the phase error    information received from the first IC.

6. A method of operation within a signaling system, the methodcomprising:

-   -   generating a strobe signal within a first integrated (IC) device        by delaying an aperiodic timing signal for a first time        interval;    -   outputting the strobe signal and a data signal from the first IC        device to a second IC device;    -   sampling the data signal within the second IC device at times        indicated by the strobe signal to generate phase error        information;    -   outputting the phase error information from the second IC device        to the first IC device; and    -   adjusting the first time interval within the first IC device in        accordance with the phase error information.

-   7. The method of clause 6 wherein sampling the data signal within    the second IC device at times indicated by the strobe signal to    generate phase error information comprises:    -   sampling the data signal in response to the strobe signal to        generate a sequence of data samples; and    -   sampling the data signal in response to a phase-shifted version        of the strobe signal to generate a sequence of edge samples.

-   8. The method of clause 7 wherein sampling the data signal within    the second IC device at times indicated by the strobe signal to    generate phase error information further comprises comparing each of    the edge samples with one of the data samples captured before the    edge sample and with one of the data samples captured after the edge    sample, and signaling a first type of timing error for each edge    sample that does not match the data sample captured before the edge    sample and a second type of timing error for each edge sample that    does not match the data sample captured after the edge sample.

-   9. The method of clause 8 wherein sampling the data signal within    the second IC device at times indicated by the strobe signal to    generate phase error information further comprises generating a    phase error signal in either a first state or a second state    according to whether more timing errors of the first type or the    second type are signaled over an error detection interval.

-   10. A memory controller comprising:    -   a first delay circuit to delay an aperiodic timing signal for a        first interval to generate a strobe signal;    -   a transmit circuit to output the strobe signal and a        corresponding data signal to a memory device;    -   an interface to receive error information from the memory        device, the error information indicating a phase error between        the strobe signal and the data signal; and    -   timing control circuitry to adjust the first interval in        response to the error information.

-   11. The memory controller of clause 10 wherein the first delay    circuit comprises an input to receive a delay control value from the    timing control circuitry, and circuitry to apply the delay control    value to establish the first interval.

-   12. The memory controller of clause 11 wherein the timing control    circuitry includes a delay control update circuit to increase or    decrease the delay control value according to the error information    received from the memory device.

-   13. The memory controller of clause 10 further comprising a data    delay circuit to delay the data signal for a second time interval    before the data signal is output to the memory device.

-   14. The memory controller of clause 13 wherein the timing control    circuit comprises circuitry to adjust the second interval in    response to the error information.

-   15. A method of operation within a memory controller, the method    comprising:    -   delaying an aperiodic timing signal for a first interval to        generate a strobe signal;    -   outputting the strobe signal and a corresponding data signal to        a memory device;    -   receiving error information from the memory device, the error        information indicating a phase error between the strobe signal        and the data signal; and    -   adjusting the first interval based on the error information.

-   16. The method of clause 15 further comprising:    -   delaying the data signal for a second interval before outputting        the data signal to the memory device; and    -   adjusting the second interval based on the error information.

-   17. The method of clause 15 wherein delaying the aperiodic timing    signal for a first interval comprises establishing, within a delay    circuit, a propagation delay that corresponds to the first interval.

-   18. The method of clause 15 wherein adjusting the first interval    based on the error information comprises increasing or decreasing    the propagation delay within the delay circuit.

-   19. The method of clause 18 wherein increasing or decreasing the    propagation delay within the delay circuit comprises incrementing or    decrementing a delay control value that is applied within the delay    circuit to control the propagation delay.

-   20. A memory controller comprising:    -   means for delaying an aperiodic timing signal for a first        interval to generate a strobe signal;    -   means for outputting the strobe signal and a corresponding data        signal to a memory device;    -   means for receiving error information from the memory device,        the error information indicating a phase error between the        strobe signal and the data signal; and    -   means for adjusting the first interval based on the error        information.

While the invention has been described with reference to specificembodiments thereof, it will be evident that various modifications andchanges may be made thereto without departing from the broader spiritand scope of the invention. Accordingly, the specification and drawingsare to be regarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. An integrated circuit (IC) memory controller,comprising: a strobe enable circuit to receive an external strobe signalfrom a memory device, the strobe enable circuit including gatingcircuitry to generate a gated strobe signal based on a phaserelationship between a read enable signal and the external strobesignal; a receiver circuit to receive the gated strobe signal and readdata from the memory device, wherein the read data is accompanied by theexternal strobe signal; and adaptive calibration circuitry to, during alive data transfer mode of operation, adaptively adjust at least one ofa first relative alignment between the read enable signal and theexternal strobe signal, and a second relative alignment between thegated strobe signal and the read data.
 2. The IC memory controller ofclaim 1, wherein the adaptive calibration circuitry includes:oversampling circuitry to generate error information, the adaptivecalibration circuitry to adaptively adjust the at least one of the firstrelative alignment and the second relative alignment based on the errorinformation.
 3. The IC memory controller of claim 2, wherein: theoversampling circuitry is to oversample the gated strobe signal with areference clock signal to generate the error information as first errorinformation for the first relative alignment.
 4. The IC memorycontroller of claim 3, wherein the adaptive calibration circuitry is toadaptively adjust the first relative alignment by delaying the readenable signal with respect to the external strobe signal in response tothe first error information.
 5. The IC memory controller of claim 2,wherein: the oversampling circuitry is to oversample the read data togenerate the error information as second error information for thesecond relative alignment.
 6. The IC memory controller of claim 5wherein the adaptive calibration circuitry is to adaptively adjust thesecond relative alignment by delaying the read data with respect to thegated strobe signal in response to the second error information.
 7. TheIC memory controller of claim 1, embodied as a dynamic random accessmemory (DRAM) controller.
 8. A method of operation in an integratedcircuit (IC) memory controller, comprising: receiving an external strobesignal from a memory device; generating a gated strobe signal with astrobe enable circuit, the gated strobe signal based on a phaserelationship between a read enable signal and the external strobesignal; receiving the gated strobe signal from the strobe enablecircuit, and receiving read data from the memory device, wherein theread data is accompanied by the external strobe signal; and during alive data transfer mode of operation, adaptively adjusting at least oneof a first relative alignment between the read enable signal and theexternal strobe signal, and a second relative alignment between thegated strobe signal and the read data.
 9. The method of claim 8,wherein: the adaptively adjusting at least one of the first relativealignment and the second relative alignment is based on errorinformation.
 10. The method of claim 9, further comprising: oversamplingthe gated strobe signal with a reference clock signal to generate theerror information as first error information for adaptively adjustingthe first relative alignment.
 11. The method of claim 10, wherein theadaptively adjusting the first relative alignment further comprises:delaying the read enable signal with respect to the external strobesignal in response to the first error information.
 12. The method ofclaim 9, further comprising: oversampling the read data to generate theerror information as second error information for the second relativealignment.
 13. The method according to claim 12, wherein the adaptivelyadjusting the second relative alignment further comprises: delaying theread data with respect to the gated strobe signal in response to thesecond error information.
 14. The method according to claim 8, furthercomprising: receiving the external strobe signal and the read data inaccordance with a dynamic random access memory (DRAM) protocol.
 15. Anintegrated circuit (IC) chip, comprising: memory control circuitryincluding receiver interface circuitry to receive an external strobesignal from a memory device, the receiver interface circuitry includinggating circuitry to generate a gated strobe signal based on a phaserelationship between a read enable signal and the external strobesignal, the receiver interface circuitry to receive read data from thememory device, wherein the read data is accompanied by the externalstrobe signal; and adaptive calibration circuitry to, during a live datatransfer mode of operation, adaptively adjust at least one of a firstrelative alignment between the read enable signal and the externalstrobe signal, and a second relative alignment between the gated strobesignal and the read data.
 16. The IC chip of claim 15, wherein theadaptive calibration circuitry includes: oversampling circuitry togenerate error information, the adaptive calibration circuitry toadaptively adjust the at least one of the first relative alignment andthe second relative alignment based on the error information.
 17. The ICchip of claim 16, wherein: the oversampling circuitry is to oversamplethe gated strobe signal with a reference clock signal to generate theerror information as first error information for the first relativealignment.
 18. The IC chip of claim 17, wherein the adaptive calibrationcircuitry is to adaptively adjust the first relative alignment bydelaying the read enable signal with respect to the external strobesignal in response to the first error information.
 19. The IC chip ofclaim 16, wherein: the oversampling circuitry is to oversample the readdata to generate the error information as second error information forthe second relative alignment.
 20. The IC chip of claim 19 wherein theadaptive calibration circuitry is to adaptively adjust the secondrelative alignment by delaying the read data with respect to the gatedstrobe signal in response to the second error information.